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The smaller members of the felid family can purr, but why? Hank takes on this most adorable of life's mysteries in todays episode of SciShow.

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Have you ever been lying in bed and trying to sleep when suddenly the cat jumps up on your chest and starts like kneading you, getting all up in your face, rumbling like a Corvette and drooling into your mouth? And you're kind of annoyed because like you don't love the taste of cat spit and, you have to get up early; but you're also like "Aww, that's very cute. This cat has genuine affection for me." Well, don't be fooled. Sheriff Fluffy is probably happy to be cuddling you, but cats don't just purr when they're content, they also do it when they're in pain, giving birth, and even dying. 

(Intro music plays)

The smaller members of the felid family--including lynx, cougar, ocelot, and domestic cat-- can purr, and they do it by pulsing muscles in their larynx and diaphragm. The resulting vibrations come in a rhythmic pattern during both inhalation and exhalation at a frequency between 25 and 150 hertz. 

Cats make all kinds of interesting sounds: hisses, growls, mews, meows, and mroooow (which is one of my favorites), all communicating specific feelings like "feed me" or "you better recognize," while purring could mean "I'm so happy" or "crap. I'm dying." Since purring occurs in such different emotional states, it's not considered a true communicative vocalization. Instead, it turns out it's a kind of self-medication. Veterinarians have long known that cats are quicker to heal than dogs, especially from bone trauma. It's not uncommon for distracted cats to fall from upper-level windows in a condition known as high rise syndrome, but what's incredible is that these poor broken cats have a 90% chance for survival, no matter how messed up they are, in part because they have a built-n method of physical therapy.

In the late 1990's, Dr. Clinton Rubin of the state university of New York and his colleagues discovered that exposure to low-level frequencies helps build bone density, and a cat's purr falls exactly within that frequency's sweet spot. So it could be that cats' purring helps cats heal and keep them healthy. And people who have gone through physical therapy can attest to this--sitting there purring sure beats the other way to build bone density: actually moving around. 

Let's face it: cats are kinda lazy, and purring may help take the place of good, old fashioned exercise. Other animals need to like run after balls or chase cars to maintain healthy bones, but a cat need only put up its paws and purr. And those perfect hertz vibrations may help humans too. Turkeys, rats, and sheep strapped to vibrating plates at purr frequency for 10 to 20 minutes a day showed a marked increase in bone strength. Researchers are now looking into how this technology could benefit astronauts who suffer bone density loss under low gravity conditions in space.

Maybe Canadians Jack and Donna Wright, the dubious world record holders for most cats owned by one household should call NASA, because they have 689 cats. Six hundred and eighty-nine. I'm just picturing a mountain of cats, all in one enormous beanbag, just rehabilitating visiting astronauts... with their positive vibrations. So crazy, it just might work. Also, who cares? It's adorable. 

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