CURLING UP WITH your favorite ball of fur as she purrs away is pretty close to heaven, at least for cat folk. Yet, hidden between those vibrations, that most appealing of domestic sounds remains wrapped in mystery, and even a little magic. No one is certain exactly why cats purr, though there are a number of good guesses. The obvious observation is cats seem to purr when they’re pleased and feeling good. But that’s not always the case: Some cats also purr when they’re hungry, injured, or frightened. And most surprisingly, purring frequencies have been shown to stimulate bone regeneration—yes, bone regeneration. Cats purr by using their larynx and diaphragm muscles, both as they inhale and as they exhale, although just how the central nervous system generates and controls those contractions isn’t yet understood. Early 19th century taxonomists thought cats could either purr or roar, and split the family Felidae along these lines—“purrers’ (subfamily Felinae) and ‘roarers’ (subfamily Pantherinae). Today, though, taxonomists believe most cats can purr, with a few probable (though not certain) pantherine exceptions: lion, leopard, jaguar, tiger, snow leopard and clouded leopard. (Cheetahs and cougars? Yeah, they purr.) So, why do it? If it’s a form of communication, it’s meant for those near and dear, since cats purr at a frequency and volume too low to travel far. Purring (and many other low-frequency vocalizations in mammals) often are associated with positive social situations: nursing, grooming, relaxing, being friendly. More likely, though, purring is simply soothing, or self-soothing, as cats may also purr in stressful situations. In that case, purring would be akin to how humans soothe themselves by crying, laughing, distracting themselves, or even organizing their desk. Some veterinarians and cat enthusiasts have observed cats lying alongside each other and purring when one is injured (a behavior termed “purr therapy”), though scientific literature on the subject is scant. Beyond being calming for the injured kitty, “purr therapy” may have bone healing properties. Domestic cats purr at a frequency of about 26 Hertz, in a range that promotes tissue regeneration. That’s not as crazy as it sounds: High-impact exercise promotes bone health for the same reason, because bones respond to pressure by making themselves stronger.
Read More: WIRED