Purring is the most common sound cats make. Yet we know less about it than meowing, chirping, chattering, hissing, and growling.
Yes, cats purr when they're content. When yours is curled up in the sun, you may hear a gentle rumble as he breathes in and out. Touch him, and you feel a little quiver. It's almost as if he's sending out waves of calm.
Bob, a Maine Coon mix, was never fond of the ride to the veterinarian. While the cat would purr placidly through the vet's exam, he pitched a fit and cried during the trip there.
"Riding in a car stressed him out terribly," says owner Sandy Volkman of Lakeville, Minn.
When Bob went into kidney failure at age 18, Volkman couldn't fathom driving him to be put down through her tears and his cries. Her veterinarian recommended Minnesota Pets, a Twin Cities-based mobile euthanasia service.
But you shouldn't assume that sound means your cat is in a good mood. Or that it's the only time you'll hear it. Cats purr to communicate other emotions and needs, too.
What if you pick your cat up and hold him? Does he purr because he likes it -- or because he's nervous?
Although you'll never know exactly what yours is saying when he purrs, research from animal experts, along with considering the situation, lets you make an informed guess.
Your cat looks relaxed: Perhaps she's on her back, eyes half-closed, tail mostly still. If she's purring, it's safe to assume she's in her happy place.
That noise is a big smile.
He's Hungry or Wants Something
Some cats purr when it's mealtime. British researchers studied the sounds that house cats make when they're hungry and when food isn't on their minds. The purrs don't sound the same.
When cats purr for food, they combine their normal purr with an unpleasant cry or mew, a bit like a human baby's cry. Experts believe that we're more likely to respond to this sound. They've found that people can tell the difference between the purrs, even if they aren't cat owners.
Kittens can purr when they're only a few days old. It's probably a way to let their mothers know where they are or that they're OK.
Purring also helps a kitten bond with its mother. Mama cats use it like a lullaby.
Relief and Healing
Even though purring takes energy, many cats purr when they get hurt or are in pain. So what makes the effort worth it?
It might simply be a way for a cat to soothe itself, like a child sucks their thumb to feel better.
But some research suggests that purring actually helps cats get better faster. The low frequency of purrs causes a series of related vibrations within their body that can:
Heal bones and wounds
Build muscle and repair tendons
Lessen pain and swelling
This might explain why cats are able to survive falls from high places and tend to have fewer complications after surgeries than dogs.