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5 Sounds You Probably Can't Hear

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Think you have perfect hearing? There are still plenty of sounds in the world that you can’t detect. The low range of human hearing starts around 20 hertz, and tops out at about 20,000 [PDF]. By contrast, bats can hear ultrasonic sounds with frequencies up to 110,000 hertz. Other animals, like elephants, hear sounds many times lower than those a human can perceive. And as people age, their hearing gets even worse, eliminating even more sounds from the range of audible noises. Here are just a few sounds most people are missing out on: 

1. Sounds for young people 

As humans age, their hearing changes. Age-related hearing loss, called presbycusis, means that older people can’t hear some high-pitched sounds they would have heard in their youth. Most people over the age of 18 cannot hear the 17,400 hertz tone in the video above. 

2. Music designed for cats

In 2014, activists from Pussy Riot rigged an electric piano to play music designed specifically for cats. Cats possess ultrasonic hearing, meaning they can hear a much wider frequency of sounds than humans (or most other mammals, for that matter) can [PDF]. Although people could hear portions of the concerto Pussy Riot staged to protest Internet censorship, the melody is a whole lot more complex from the feline point of view. For what it's worth, the cats seemed to enjoy it. Research has shown that cats are pretty into feline-specific tunes, in general. (We have some video evidence.) 

3. A dog-specific Beatles’ song

In the Beatles’ song “A Day in the Life,” the band included a whistling noise at a frequency of 15,000 hertz right after the last chord of the song, designed to be heard by canine Beatles fans. “We’d talk for hours about these frequencies below the sub that you couldn’t really hear and the high frequencies that only dogs could hear. We put a sound on Sgt. Pepper that only dogs could hear,” Paul McCartney told the BBC in 2013. (The sound starts just after the 5-minute mark.)

4. Ultrasonic finger friction

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When you gently rub your thumb and index finger together, the friction creates an ultrasonic signal [PDF]. The action is a useful way to test out the function of a bat detector, which converts ultrasonic sound from bat echolocation into noise humans can hear. In the book Insects Through the Seasons, entomologist Gilbert Waldbauer writes that pet bats can be trained to respond to the sound, and fly toward it. 

5. Infrasonic elephant calls 

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Elephants can hear and make sounds well below human range, to as low as 14 to 16 hertz. They can also produce these infrasonic calls at extremely high volumes, around 85 to 95 decibels. For comparison purposes, 95 decibels is the equivalent of the noise of a subway train from 200 feet away. These loud, low sounds allow elephants to keep in touch with each other over distances of more than a mile. Listen to an example of these elephant rumbles from the Elephant Listening Project

See Also: 9 Strange Sounds No One Can Explain

[h/t: reddit

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Listen to the Impossibly Adorable Sounds of a Baby Sloth
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Sometimes baby sloths seem almost too adorable to be real. But the little muppet-faced treasures don't just look cute—turns out they sound cute, too. We know what you're thinking: How could you have gone your whole life without knowing what these precious creatures sound like? Well, fear not: Just in time for International Sloth Day (today), we have some footage of how the tiny mammals express themselves—and it's a lot of squeaking. (Or maybe that's you squealing?)

The sloths featured in the heart-obliterating video below come from the Sloth Sanctuary of Costa Rica. The institution rescues orphaned sloths, rehabilitates them, and gets them ready to be released back into the wild.

[h/t The Kid Should See This]

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