Exactly how and why cats purr is still mostly a mystery. The cats I’ve loved have done it when they’re happy. But that’s not the only time domesticated cats do it, according to this informative article in The Atlantic by Katherine J. Wu.
On the not-so-infrequent nights when I’m plagued by insomnia, no combination of melatonin, weighted blankets, and white noise will do. Just one cure for my affliction exists: my cat Calvin, lying atop my shoulder, lulling me to sleep with his purrs.
For veteran members of Club Purr, the reasons are clear. A purr is warm tea, a roaring fire, and fresh-out-of-the-oven cookies, all rolled into a fleece-lined hug; it is the auditory salve of a babbling brook; it is coffee brewing at dawn. It is emotional gratification incarnate—a sign that “we’ve made our pets happy,” which just feels darn good, says Wailani Sung, a veterinary behaviorist at the San Francisco SPCA.
But purrs—one of the most recognizable sounds in the animal kingdom—are also one of the most mysterious. “No one, still, knows how purring is actually done,” says Robert Eklund, a phonetician and linguist at Linköping University, in Sweden. Nor can experts say, exactly, what purring means. Cats purr when they’re happy—but also sometimes when they’re anxious or afraid, when they’re in labor, even when they’re about to die. Cats are perhaps the most inscrutable creatures humans welcome into our homes, and purring might be the most inscrutable sound they make.
There is, at least, some consensus on what purring is. In the strictest sense, the sound is a rhythmic, rumbly percolation that’s produced during both exhales—as is the case with most typical animal vocalizations—and inhales, with no interruptions between. Purrers also run their motor with their mouths entirely closed, like little feline ventriloquists; the sound simply springs out of the body at a frequency that roughly spans the range between 20 and 150 Hertz. Back in the 1960s, one scientist posited that purring was the product of blood percolating through the vena cava, a vessel that returns the body’s blood to the heart; that notion was later disproved. Now it’s generally understood that the source is the voice box: The brain pings electric signals to the vocal folds, prompting them to flutter open and shut like little muscular doors.
I did not know that there have also been some efforts toward trying to find out if the specific sounds produced by purring cats might have healing properties. After all, many of us have been sick and have discovered the sound of our purring cat next to us actually made us feel and sleep better.
Wu notes in this article that there have been no breakthroughs in research on whether purring has palliative properties based on the tone, resonance, etc. of cat purrs. It might be simply that cat purring makes us feel loved, and in doing so has positive psychosomatic effects that are still difficult to quantify — i.e., to be able to say, as one scientist puts it in the article, “I sat with a purring cat on my broken leg for 15 minutes a day; I healed more rapidly than someone else.”