What’s That Mysterious Sound?

What’s That Mysterious Sound?

Just when you think you’re starting to fully understand the nuances of animal communication, the cat starts to purr. Although cats have been sharing our homes for thousands of years, we are still unsure of why and how they make that soothing sound that is unique to their species—the purr.

While many wild animals have the ability to make a similar noise, only the domestic cat and a couple of other smaller felines (the bobcat, lynx, and cheetah) can produce a genuine purr—a sustained sound that’s emitted on both inhalation and exhalation. As it turns out, felines that can roar (lions and leopards, for example) are unable to purr, and vice versa. This distinction is thought to be related to bone and cartilage structure in the voice box, but the specific mechanism is not fully understood.

How, exactly, is a purr generated? One reasonable theory is that the soft tissues in the voice box are tightened and relaxed in a cyclical fashion. That seems pretty simple until you consider the fact that the sounds of purring repeat at a frequency of 25-50 times every second. Tensing a muscle at that rate would be quite a feat! Don’t forget that cats can produce a variety of other vocalizations using those muscles while in the process of purring. The jury is still out on how feline anatomy and air flow can interact in such a complicated way.

Of course you know that cats purr when they’re happy and comfortable, grooming a friend or snuggled up on the lap of a gentle person who won’t disturb them too much, touch them too long, or otherwise impinge on their highly specific list of demands. Mothers do it when they are cleaning and nursing their newborns, and kittens develop this skill at the age of two or three days; that makes it a handy way for caregiver and infant to communicate in close quarters. Unexpectedly, though, cats may purr when faced with daunting situations like meeting a larger, more powerful cat or undergoing a veterinary exam. Cat behaviorists theorize that, in these cases, purring is analogous to the human smile or giggle. Although we display a smile when we are happy, a slightly different version of it may appear unbidden when we are stressed and anxious, even fearful. Stranger still, it’s not so unusual for a cat to purr when he is suffering intense pain or even in the process of dying. One wonders whether this version of the purr might function as a self-soothing mechanism, similar to a distressed child that’s observed humming quietly, hugging themselves, or repeating a comforting phrase over and over. Some researchers also speculate that the act of purring may stimulate endorphin release, thus easing the misery of a suffering cat.

The purr is a deceptively simple sound that cat owners hear many times a day, but there’s actually very little known about the mechanism and meaning of it. Once again, the cats have managed to keep us guessing.

Dr. M.S. Regan