When a purring cat rubs against you, you can’t help but feel pleased with yourself for being so lovable. But don’t move on from petting that kitty to patting yourself on the back just yet. Happiness isn’t the only thing that makes cats purr.
Sure, you might hear purrs when your pet feels relaxed or friendly, but cats also purr when they’re hungry, stressed, or in pain. “All behavior depends on history, context and expectation,” Tony Buffington, a cat expert and veterinarian at Ohio State University, told Wired. “So it’s naive to think that cats can only purr for one reason—it’s like thinking that people can only laugh for one reason.” Like how some guffaws are a reaction to humor while other giggles could come from nerves, cats’ purrs are open to interpretation.
Mother cats purr to lead their kittens—which are blind and deaf when they’re born—to them for food and warmth. In turn, vets believe, kittens purr to show they’re okay and help them bond with mama cat.
Purrs release feel-good endorphins, so experts think cats use the vibrations to soothe themselves. That could mean purring while enjoying some cozy cuddles from their owner, or it might help calm their nerves—or literally heal their pain. Studies have found that whole-body vibrations of 35 to 50 Hz could help stimulate bone healing. Cats’ purr frequencies range from 25 to 150 Hz, and some suggest the vibrations could help kitties keep their skeletons strong. (Sounds crazy, but even NASA astronauts have used vibration therapy in space, where lack of gravity means no bone-healthy weight-bearing exercise.)
As for purr frequencies go even higher than150 Hz, those serve an entirely different purpose. One study in the journal Current Biology found that when cats were trying to get their owners to feed them, their purr frequency shot up to 220 to 520 Hz—awfully close to the 300 to 600 Hz of a human infant’s cry. Researchers suggest the higher frequency makes the sound harder for cat (and baby) parents to ignore.
Bottom line: Not all purrs are created equal. The best way to figure out your cat’s message is by looking at what else is going on. At dinnertime, your furry friend might have food on the brain. But a kitty curled up on your lap is probably just enjoying your company.