The thrumming, rumbling sound coming from a cat as she inhales and exhales is one of life’s great delights — and mysteries. Theories about purring are as varied as the markings on a calico. Domestic cats purr when they’re content, often when we’re stroking their chins or heads, or opening a can of food. Mother cats purr so their helpless newborn kittens can find them (and the source of dinner), and often purr while nursing. But cats also purr in times of stress — when they’re recovering from an injury, or at the vet’s office. Some cats purr so loudly during a checkup, the vet can’t clearly hear the cat’s heartbeat through his stethoscope.
Scientists say that a cat’s purr results from intermittent signaling by the diaphragmatic (diaphragm) and laryngeal (larynx or voice box) muscles, at a frequency of 25 to 150 Hertz (a Hertz being one cycle per second). Research suggests that sound frequency of this range can promote healing and bone growth. There’s no definitive answer yet, and the power of the purr is still a puzzle. Clinically, we may know how cats purr, but why? They may purr simply because…they can.