Tag: Health

Insights from a Visit to the Civil War Medical Museum | March 10 2026, 15:59

Today a big interesting historical post.

Where I was: Historical Museum of Military (Civil War) Medicine in Frederick, MD. Entry is $9, $15 with a guide. For an hour and a half, we got a very smart guy who gave an interesting lecture, making the provincial museum really very interesting. We even tipped the guy afterward.

A few interesting facts that I didn’t know before. During the Civil War in the USA (1861-1865), there was a monstrous scale of losses – over 600,000 people. One in every ten was mobilized for the war. That is, excluding women, children, and the disabled – yes, someone from almost every family fought.

Apparently, Americans were not very experienced in wars back then, and organizing large groups of people was based on the “fend for yourself” principle. From gastrointestinal diseases alone, nearly four times more people died than from wounds. Soldiers cooked everything themselves – there was no cook or porridge for the platoon. They split into micro-groups of a few people, pooled whatever they had, and fried it on a fire. For some reason they mainly fried, not boiled (which also contributed to diseases). Their main rations were salt pork and hard-tack — crackers as hard as a stone. Fried hard-tacks were called Skillygalee.

Remember, it was not like that in European wars. And all because there were many of them, and they quickly figured out how to make them more effective. Plus, there was also a civil war, poorly organized and spontaneous.

Initially, soldiers were handed money in the field and they sent it to their families as best they could (not all reached its destination). For Southerners, money devalued faster than they could carry it to the tent. Back then, each state issued its own money. They write about 8000 different banknotes at that time. I didn’t quite believe it, started researching, and it turned out that this is still a very conservative estimate. Yes, anyone (state, city, private bank, railway, factory, and even a pharmacy) could print their own paper money. Each bank issued banknotes of its own design for different denominations ($1, $2, $3, $5, etc.). In 1860, there were about 1600 private banks in the USA, and almost each issued its own range of notes. But in the end, greenbacks – federal money prevailed.

They also told us about Dorothea Dix, the head of army nurses for the Union. She introduced an interesting age standard for the nurses. No “young and beautiful.” Only women over 30 years of age, “plain-looking,” no jewelry, fashionable dresses, or crinolines – only strict brown or black dresses. At that time, the appearance of a woman in a male military camp was considered almost indecent. Dorothea wanted the soldiers to see in the nurses strict mothers or aunts, not objects of flirtation.

To join the army, a volunteer was required to have at least two teeth opposing each other. Why? A soldier needed to quickly bite off the tip of a paper cartridge to pour the powder into the barrel. No teeth — you’re useless in battle.

Back then, they shot with Minié balls – made of soft lead. It was huge caliber (thumb-sized) and when it hit the body, it didn’t just pass through, it “burst” and literally turned bone into fine crumble. Repairing such a bone was impossible, so amputation became the only way to save a person from gangrene. At least there was some form of anesthesia (chloroform/ether).

Before the Civil War in the USA, people were buried where they died. But the war generated a demand: affluent Northern families wanted to bring their sons’ bodies home. That’s when embalming flourished. Right behind the front line were tents of “embalming surgeons” who for a decent sum (about $50–$100 for an officer) extracted blood and injected chemicals (arsenic and zinc) into the body. Actually, the museum building included such a place. Lincoln’s body after his assassination was transported across the entire country on a train, and it looked “alive” thanks to this new technology, which became the best advertisement for the new industry.

Overall, Frederick is a very nice city, full of art and nonconformists 🙂 Like our Leesburg, but 20 times bigger.

P.S. It was interesting to study what drove people to go die. Of course, our guide said “patriotism”.

But if you google, it turns out not quite so. Of course, in 1861 no one knew that the war would last 4 years and take 600,000 lives.

Reason #1 – boredom. Life on a farm in the mid-19th century was incredibly monotonous. War seemed like the greatest adventure in life. Guys thought: “I’ll go, see the world, shoot, become a hero, and then return to harvest.”

Reason #2 – naivety. The first volunteers went to the front as if on a picnic. In the first major battle (Bull Run), civilians from Washington even came with picnic baskets to watch the “spectacle,” until they were swept away by the retreating crowd of bloodied soldiers.

Reason #3 – “honor.” In the 19th century, “honor” was not an empty word. If you were a healthy guy and didn’t go to the army, you became an outcast in your own town. It’s written that girls often refused to go out with those who didn’t wear a uniform.

Reason #4 – “regimental solidarity.” As I already said, regiments were formed from neighbors. Not going to war meant betraying your friends, brothers, and father. Shame before neighbors was stronger than the fear of death.

What did they fight for?

Here the goals of the North and South radically differed:

For the North, the main idea was “Integrity of the Union.” For them, the USA was a great experiment in democracy that could not be allowed to fail. The slogan “Save the Union” was more powerful than “Free the Slaves.” At first, not everyone was ready to die for abolition of slavery.

For the South (Confederacy), the main motivation was “Defending their homes.” Most Southern soldiers did not own slaves (slavery was too expensive a luxury for ordinary farmers). But they were convinced that the “Yankee northerners” were coming to seize their land, burn their homes, and impose their rules. They saw themselves as heirs of Washington, fighting against “tyrant” Lincoln.

Reason #5 – bounties

When initial enthusiasm faded (by 1863), pure calculation played its part. States and the federal government started paying huge “enlistment bounties.” A sum of $500–$1000 was equivalent to a few years’ earnings for a laborer. For a poor immigrant (Irish or German) just off the boat in New York, it was a chance to provide for a family or buy a farm after the war.

In 1862-63, both sides introduced the draft, as volunteers were running out. This exposed social injustice.

In the North, you could officially avoid the army by paying $300 (huge money for a poor man, but manageable for the middle class) or find a “substitute” (a person who would fight in your place for money).

In the South, there was the “Twenty Negro Law.” Owning 20 or more slaves exempted you from service, as you were “needed in the rear for production control.”

This caused fierce resentment among ordinary soldiers. The famous “Draft Riots” in New York (1863) were sparked precisely by this sense of injustice.

So there you have it 🙂

Understanding Fever: A Physiological Defense Mechanism | February 17 2026, 09:00

I’ve only slightly (hopefully) gotten sick here and realized during the process that many people around me take pills for a minor onset of fever, considering it normal.

I’m sharing my understanding of the process, which should be very close to scientific. When an infection penetrates the body, foreign bacteria or viruses enter the bloodstream, which the immune system attacks. During the attack, signaling molecules are produced, the purpose of which is to declare a general alert throughout the body. Specifically, cytokines are produced, which also inform the brain (hypothalamus) that action is needed. Pyrogens (fever-inducing agents) include cytokines and external pathogens. The hypothalamus activates a fever through the synthesis of prostaglandins. Why: at a temperature of 38.5°C, the immune system becomes more active, antibodies are produced in larger amounts, microbial reproduction slows down, and some viruses do not reproduce.

If you consume, for example, Ibuprofen, it blocks the enzyme (COX) that creates these prostaglandins. Meaning, the pyrogens are still in the blood, but the brain “can’t hear” them and doesn’t raise the temperature.

There are only two cases when you should reduce fever: if you truly feel awful, have a severe headache, vomiting, etc. Unnecessary stress does not help the body. And if the temperature exceeds 39°C. At that point, the harm from high temperature outweighs the benefits. Even then, there are so many “buts” that a doctor should make the decision. For example, if the heart is problematic, these are special cases.

Oh, here’s something else interesting. Why when the temperature is high you feel “cold” and want to cover up. In the hypothalamus itself, there’s something like a thermostat, normally set to 36.6°C. When pyrogens arrive, it raises the temperature through prostaglandins, but since it’s the brain, it immediately cranks up its own “normal temperature” in its thermostat to, say, 38.5°C. As a result, a body temperature of 37°C suddenly feels low, and it feels like “it’s cold around, need to cover up.” Covering up is passive thermal insulation, and generally, it helps to more quickly raise the temperature to the target level. Later, when the temperature reaches 38.5°C, the chills may disappear (unless the hypothalamus further raises its thermostat). And when the temperature plateaus, around 38.5°C, covering up is harmful.

When the temperature starts to drop back, the internal thermostat switches to 36.6°C, and to cool down faster, the body produces sweat. So, if you’re sweating, it’s a sign of recovery.

(Well, what else is there to do at four in the morning, when because of all this, I can’t sleep)

Exploring the Delights of Origin Thai Spa: More Than Just Massage | January 08 2026, 23:48

We bought all this at our Thai massage salon Origin Thai Spa today for $20 — slices of matum tea, Bael Fruit Tea. To the left of it — pandan tea. Also, before buying we tried some hand-made cakes (delicious!).

The salon is staffed by Thai women, all of them elderly, many speak English poorly, but they all know their massage craft very well. We are regular customers there with a membership, and I highly recommend the salon to locals. Thai massage is not for everyone, though, because when done correctly, it is quite painful during the process (but beneficial, and feels like it recharges all your internal batteries).

Dangerous Beauty: The Spiked Palms of Costa Rica’s Jungles | January 03 2026, 02:35

A very typical palm for Costa Rican jungles. Hugging one of these is a bad idea. These black spikes are incredibly sharp, hard, and can reach lengths of 10-15 centimeters. They are arranged in dense rings along the entire trunk. The most treacherous thing about these spikes is their fragility and dirt. If a person or animal runs into such a spike, the tip easily breaks off and remains deep in the wound. Since in the tropical climate these needles are home to millions of bacteria and fungi, a deep splinter almost guarantees a serious, painful, and slow-healing inflammation.

The density of the needles varies, sometimes the trunk is not visible behind them.

Such was the case in the series Pluribus.

Navigating the Airline Seat Dilemma: Equality and Passenger Size Policy Changes | December 30 2025, 20:21

As I sit on the plane, I ponder how airlines separate excessively obese people from those not obese enough, and how they make the former pay twice as much. And how does this align with the policy of universal equality and equal opportunities? The issue causes “anthropometric dissonance” – over the past decades, the average airplane seat width has narrowed from 47 to 43 cm, while the average passenger weight has significantly increased. As a result, there emerges a rigid classification of passengers into “regular” and officially recognized “Customers of Size” (CoS).

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The main technical criterion separating these categories is the “armrest rule.” If a person’s body extends beyond the outer boundary of the lowered armrest by more than 1 inch (2.5 cm), they are officially recognized as “oversized.” The inability to fully lower the armrest without pain or discomfort to oneself or a neighbor is grounds for requiring the purchase of a second seat.

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Until 2025, Southwest Airlines was considered the “gold standard” for large individuals, allowing them to occupy a second seat for free. However, as of January 27, 2025, the rules changed: such passengers are now required to purchase a second seat in advance when booking. If an individual fails to do this and the flight is full, they may simply be denied boarding and offered to rebook to another flight where two adjacent seats are available.

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The financial risks now almost entirely fall on the passenger. According to the new 2025 policy, a refund for an additionally purchased seat is only possible if the flight departs not fully booked. Considering that the average aircraft occupancy today is 85–90%, the likelihood that money paid for a “comfort seat” will not be refunded is extremely high.

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There exists a “geographical lottery” of passenger rights in the world. In Canada, a unique doctrine of “One Person, One Fare” (1P1F) is affirmed by court. There, obesity is recognized as a “functional disability,” therefore, airlines are required to provide a second seat for free on domestic flights if the passenger presents a medical certificate. In the USA and Europe, no such benefits exist, and comfort is considered a commercial service.

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Technically, there is also a “seatbelt rule,” which is the second most important (after the armrest rule) and serves as a kind of “legal and technical barrier.” Specifically, every passenger must be buckled during taxi, takeoff, and landing. If the belt does not fasten, the passenger physically cannot be seated. This isn’t a matter of comfort, but a question of legality aboard the aircraft. If the standard length of the belt is insufficient, the passenger has the right to request a seatbelt extender, which usually adds between 25 to 60 centimeters. The mere request for an extender often gets recorded by flight attendants as a marker of an “increased size passenger.” This is a critical moment. Most airlines globally explicitly forbid the use of two extenders simultaneously. If the length of one standard belt plus one extender is not enough, the passenger is recognized as “oversized” for that seat type. In this case, the airline has the full right to remove them from the flight or demand the purchase of a second seat, as safety cannot be ensured.

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Airlines’ main argument for imposing limitations is flight safety. According to EASA and FAA standards, a full airplane evacuation must take no more than 90 seconds. A large passenger, who physically does not fit in the seat, can block the aisle or slow the movement of others in an emergency, therefore they are prohibited from occupying seats near emergency exits. Personally, I think this is just a nice reason to avoid spending extra money.

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Identifying “too fat” passengers often happens right in the cabin. Flight attendants have the right to demand that a person undergo an “armrest test” in front of witnesses. If an “encroachment” into a neighbor’s space is discovered, priority is always given to those who fit in their own seat, and the CoS passenger may be removed from the flight for the comfort of others.

Night Encounter with the Fer De Lance: Survival Against the Jungle’s Deadliest Snake | December 29 2025, 18:06

Last night, I encountered the most dangerous, most venomous snake in the jungle – Fer De Lance (Bothrops asper) on a path. Generally, local clinics have antivenom and with it, the mortality rate drops to zero, but it’s better not to test it – the venom causes rapid necrosis and disrupts blood clotting. It also has a built-in night vision camera in its head. The system is so sensitive that the snake can detect a temperature difference of just 0.003 °C. This helps it hunt warm-blooded rodents and birds at night, when visual sight is limited.

It’s also super fast. Four and a half meters per second. That’s faster than you can blink. Indeed, if you’re not sitting right in front of its nose, there’s enough time for it to switch to a combat position, allowing you to jump away – so I managed to get by from behind.

Exploring Aescape: A Robotic Massage Experience | December 19 2025, 21:26

Nadia and I tried out the Aescape robot massage. Well, I was interested to see the technical side of it all. Overall, it’s quite interesting, but driving 45 minutes instead of 15 to get a robot, even if it’s slightly cheaper… not sure it makes sense to go there regularly. It’s a different story if you’re already at the gym and want a massage right now, without an appointment – it’s like a deluxe massage chair. Yes, in that case, it’s exactly what you need.

The system scans the body with four cameras on the ceiling, creates a 3D model, and then on the whole, the robot arms do a pretty good job of kneading the muscles just right, stronger in some places, gentler in others – considering the overall anatomy, and the specific person on the table. Some might wonder, won’t they accidentally maim someone due to some bug, but we drove there and back on Tesla’s autopilot, and if the cars were going to kill us, they’d have had an easier chance.

Understanding Jerusalem Syndrome and Its Global Counterparts | October 01 2025, 16:10

Listening to Sapolsky in the background, he mentioned Jerusalem Syndrome. It’s when a deeply religious American Baptist from the southern USA, having saved money and prepared, arrives in the Holy Land and sees that Jerusalem is just another city: traffic jams, smog, noise, pickpockets, McDonald’s—everything like that. And then—an interesting feature—in all cases, the person tears up sheets, takes off their clothes, and suddenly finds themselves on the streets of Jerusalem, dressed as if in a toga, begins to preach on the streets, calling for a simpler life and all that.

A psychiatric team arrives, takes the person to the hospital for a few days, everything becomes clear, they send him back home, and he never encounters this syndrome again.

Each year in Jerusalem, about up to many dozens of cases are recorded. It’s a recognized syndrome, about which scientific articles are published.

Sapolsky says that if hotels in Jerusalem always had, for example, checkered sheets instead of white ones, which seem to “invite” one to don a toga, it would help prevent the crisis.

But amusingly, there’s a twin brother of this disorder, the Paris Syndrome, which for some reason mainly affects the Japanese. Japanese tourists come to Paris because they are attracted by the culture, language, literature, and history of France, as well as the landmarks of Paris. However, once there, they encounter difficulties such as a language barrier (surprise surprise!), differences in mentality, and disappointment from the reality of Paris not meeting their expectations.

There’s also a milder version called the “Florentine Syndrome.” This often happens during a visit to one of the 50 museums in Florence, the cradle of the Renaissance. Suddenly, a visitor is overwhelmed by the depth of feeling the artist has imbued in the artwork. At this point, they acutely perceive all emotions, as if transported into the space of the image. Victims’ reactions vary up to hysteria or attempts to destroy the painting. Despite the syndrome’s relative rarity, guards in Florentine museums are specially trained on how to deal with its victims.

Overall, be careful with syndromes when you’re traveling.

PS. This image was made for me by google. In the second image, a guy in a tie tells a tearful girl 脆培, which seems just a meaningless set of characters, something like fragile culture. But when I asked ChatGPT, it told me it resembles 脱げ (nugu) — undress 🙂 if you ask Google Gemini to redo it, Google gives the same picture, where he’s also shouting 暁は, but at the same time, he has already taken off his shirt. But that’s also unclear what 暁 – it’s dawn. Generally, with Japanese, LLM is bad. I’ll leave the second image in the comments. By the way, there are several differences there, you can play a game to find ten differences. They are amusing

Echoes of Anthrax: The Amerithrax Investigation Unveiled | September 02 2025, 13:33

From the museum of the day before yesterday. Probably, some of you remember the notorious case in 2001: shortly after the 9/11 attacks, the USA experienced a series of bioterror attacks: someone mailed letters containing powder with anthrax spores (Bacillus anthracis). This led to the deaths of 5 people and infected 17, but it could have ended much worse for the entire planet. The investigation, known as “Amerithrax,” was conducted by the FBI in collaboration with other agencies and became one of the most complex in history.

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For those who might not know — the inhalational form of anthrax has a mortality rate of 85–90% without treatment. Symptoms appear after 6 days, by which time dozens will be infected. It can’t be destroyed — spores remain viable for decades in the soil. For example, on the Scottish island of Gruinard, they lingered for nearly 50 years after wartime testing. Only after 50 years had passed and after 280 tons of formaldehyde solution had been sprayed across all 196 hectares of the island, and the most contaminated topsoil around the dispersal site had been removed, did the island become relatively safe. Thus, anthrax could easily be more terrifying than a global nuclear war.

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So, returning to the subject. Initially, suspicions fell on various individuals, including Iraq or Al-Qaeda, but no evidence was found.

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The key breakthrough was scientific examination. Scientists analyzed the anthrax strain from the letters — it was the Ames strain used in American laboratories. Using microbial forensics (genetic analysis), they identified unique mutations in the spores that narrowed the source down to flask RMR-1029 in the USAMRIID (United States Army Medical Research Institute of Infectious Diseases) laboratory at Fort Detrick, Maryland.

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In other words, every living being has names and genealogy from birth, it’s just a matter of willingness to dig into the genealogy. Apparently, controlled substances have their own registry office, so to speak.

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Bruce Ivins, a microbiologist who worked there, was the custodian of this flask and had direct access (although more than 100 others did as well).

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Later, investigators gathered circumstantial evidence. Ivins had been working late at the lab just before the mailings in September and October 2001, which was inconsistent with his usual schedule. He could not convincingly explain these hours. Moreover, in early September 2001, he was vaccinated against anthrax, which seemed suspicious. The FBI also accused him of attempting to mislead the investigation: he allegedly provided false anthrax samples to divert suspicion and attempted to frame colleagues. In 2001, Ivins sent an email to colleagues offering the Ames strain for analysis, which might have been an attempt to cover his tracks.

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Behavioral signs also played a role. Ivins suffered from depression and suicidal thoughts, especially after another suspect (Steven Hatfill) was cleared in 2008. In June 2008, he was hospitalized in a psychiatric clinic, where during therapy, he made statements that the FBI interpreted as “denials without denial” — for example, that he “had no heart for killing” and did not remember participating in the attacks.

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By 2008, the investigation had narrowed down to Ivins. When he learned that charges were being prepared against him, on July 29, 2008, he took a lethal dose of Tylenol (acetaminophen). Formal charges were never brought. In 2010, the FBI officially closed the case, declaring Ivins the sole perpetrator.

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However, the conclusions remain controversial: the US National Academy of Sciences noted in 2011 that the genetic examination was not convincing enough for a definitive conclusion, and some microbiologists, victims’ families, and politicians demanded further investigation. As of now, no new discoveries have been made, and the case is considered closed.

Exploring the Boundless Spectrum: The World of Animal Hearing | August 29 2025, 17:56

From my notes as I read Ed Yong’s Immense World—

“..It is known that the range of audible frequencies for animals is different from that of humans, but I didn’t realize just how different. Imagine the highest pitch in the world—it would be just under 20 kHz, as it’s considered the upper limit of the audible range. Both the upper and lower limits tend to decrease with age. Most adults can’t hear sounds over 16 kHz. Anything above 20 kHz we call ultrasound.

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So, it turns out that our closest relatives, chimpanzees, can hear up to 30 kHz, dogs up to 45 kHz, cats up to 85 kHz, mice up to 100 kHz, and moths even up to 300 kHz. Imagine, there are so many high-frequency sounds around us, and how rich their sound world is compared to our limited one. It would be interesting to wear headphones that compress the range from 20-40000 Hz to 20-15000 Hz. Many animals, such as mice, actively use ultrasound for internal communication, beyond the hearing range of their predators.

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And when the topic of ultrasound comes up, it’s impossible not to mention bats with their echolocation. Turns out, it’s a wildly interesting topic.”

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Probably everyone knows that bats successfully hunt in caves, where no light penetrates at all, and they don’t crash into stalactites and stalagmites. There’s an English saying, blind as a bat, but actually, they can see. Some species see better, others worse. But let’s talk about echolocation.

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In general, it’s just radar. The bat screams, the sound bounces off a tree, comes back into its ears, and it gets information about how far away the tree is and whether to slow down or not. But the devil, as they say, is in the details. “Engineering” ones.

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Firstly, high-frequency sound attenuates quickly, so you need to shout very loudly for something to bounce back from a few meters away. Beyond that, bats simply don’t “see.” So, they do indeed shout very loudly, and it’s a directed scream. Specifically, they measured 138 decibels, the sound level of a jet engine if you stand next to it. But in the ultrasonic range.

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Secondly, when they scream so loudly, they need to plug their own ears so as not to kill their sensitive apparatus. It turned out that they have special muscles that block the inner ear during the scream.

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Thirdly, both they and their prey are on the move, very fast and erratic. Meanwhile, the speed of sound is about 343 meters per second. The bat’s brain must calculate the difference between the signal and the echo, taking into account both its own movement through space and the movement of the prey. It turned out that the bat’s vocal muscles can contract up to 200 times a second. Moreover, the frequency depends on the phase of the hunt. 200 times—that’s the final phase, when the moth is right in front of the nose, and tiny movements need to be tracked.

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Fourthly, the bat’s brain also has to cope with creating interference between what was shouted out two moments ago and what was shouted out a moment ago. Considering that the sound can echo off the far wall and the near branch. Plus there are waves from the cries of other bats, and they’re usually very numerous in caves. To manage this, they seem to throw a bit different modulation, plus this musculature allows them to “fire” very short pulses—a few milliseconds—and to renew pulses at their own frequency through very short intervals. Imagine what kind of computer in their brains performs the inverse Fourier transform.”

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So, all this works pretty well in small groups. But for example, the Brazilian free-tailed bats live in groups of millions. Really, together 20 million mouths shout something and wait for their echo from the walls and each other. You can’t just pick modulation and frequencies that easily, but somehow they manage. Not perfectly, and if they gather in a really big bunch in the cave, then they perform their commute to the hunt and back to the cave “by memory” – probably due to issues with echolocation. When a “door” was placed at the entrance to the cave, a bunch of bats crashed into it.

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Fifth, consider how they determine distance. It’s necessary to calculate the difference between the signal sent and the signal received (amid a bunch of noise from other bats), and for hunting, it needs to be calculated very precisely. And sound of course isn’t light, but 343 meters per second is also a lot. So studies have shown that bats can recognize differences as little as 1-2 millionths of a second, which allows them to determine distance to fractions of a millimeter. In other words, our eyes are significantly less accurate than their ears.

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Plus, a moth is actually a fairly complex 3D creation that reflects sound differently with its different parts. Otherwise, bats would eat everything that moves. They recognize. In complete darkness. A mouse’s scream contains a whole palette of frequencies, which reflect differently off parts of a moth, and the mouse’s brain somehow manages to translate this into a coherent picture. Moreover, for each of the constituent frequencies, the delay will be its own.

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Then, all this information is layered over time. Roughly speaking, a snapshot from one point is combined with a snapshot from a point a half meter to the right, then from a point half a meter forward, and so on many, many times, which enhances “sharpness” and detail. Overall, it’s the same with us – we only see the spot in front of us clearly while the rest is constructed by the brain. But the brain of a bat weighs 1-2 grams against our half kilogram.

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Think about it, you’re flying with such a built-in radar, and in front of you are two branches at the same distance, which produce essentially the same echo for their ears. And to distinguish them and understand that it’s not one object but two, you really need an advanced brain.

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So, they send pulses lasting 1-20 ms, plus longer pauses between pulses. The pulses are complex in terms of frequencies, so such bats are called frequency modulation (FM) bats. But there are about 160 species that have a much longer cry—many tens of milliseconds but with short pauses, and instead of a complex gamma of frequencies, these use a pure “note.” These bats are called CF—constant frequency. So here’s the thing with these bats—there’s a problem with the Doppler effect, which is an increase in frequency as the distance decreases. Since their brain is tuned to a strict frequency, like 87 kHz for example, they might lose their prey if the echo that reaches their ears is shifted in frequency. And what they do—they shout at a sound speed lower, so that after the Doppler effect it arrives at the correct frequency for the brain.”

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Incidentally, their radar has two modes—forward and downward, the echoes from which are processed separately. The downward radar provides information about position in space, and the forward radar—about the position in space of the prey.

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When I researched the subject, I found that yes, after 20 kHz humans hear nothing, with one exception—frequencies of 2.4 GHz and 10 GHz, which actually belong to the microwave range. Yes, humans can “hear” these frequencies, but not with the ear, but “hear.” This phenomenon is called the microwave auditory effect or the Frey effect. Initially, this effect was registered by people working near radars during World War II, and the sounds they perceived were not heard by others. It turned out that when pulsed or modulated microwave radiation was applied to areas around the cochlea, it was absorbed by the tissues of the inner ear, accompanied by their thermal expansion. In the course of this process, shockwaves are produced, perceived by humans as sound, which no one else hears. It was also discovered that with the appropriate choice of the modulating signal, it is possible to transmit information to a person in the form of individual words, phrases, and other sounds. Depending on the radiation parameters, the sound created in the head can be irritating, cause nausea, and even disable. The volume of the perceived sound can be changed, but acoustic trauma is not possible, as the eardrum does not participate in the process at all. Generally speaking, the method of specifically transmitting sonic messages that are absolutely inaudible to others opens up a whole bouquet of possibilities. I wonder if research is still being conducted on this topic. Google shows that they used to be pretty intense.”

I once published this along with a video, and Facebook reckons that if you publish a video, the text should be one, at most two lines. And in the end, almost no one saw this text. Everyone just watched the video of a bat flying around my apartment 🙂