Why Do Cats Purr?

This week on Science out of the Box, we ponder the purr. No one knows exactly why cats purr. Jacki Lyden finds out what we do know from cat expert Leslie Lyons of the University of California Davis School of Veterinary Medicine.

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A cat's purr - that warm, familiar, mellifluous, rhythmic rumbling is actually a scientific mystery. No one is quite sure why or even how they do it. Purring. That's the subject of this week's Science Out of the Box.

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LYDEN: Leslie Lyons is an associate professor at U.C. Davis School of Veterinarian Medicine. And we called her up for help with this kitten conundrum. Hello there, Dr. Lyons.

Dr. LESLIE LYONS (Associate Professor of Population Health and Reproduction, Davis School of Veterinarian Medicine, University of California): Hello. Nice to talk with you guys.

LYDEN: It's great to talk to you. Now, I have to say. I've had cats as pets. And I didn't think it was such a mystery as to why cats purred. I thought, you know, you pet the cat, it's happy, it rewards you with a little purr.

Dr. LYONS: Yes. Well, it becomes a mystery when we notice all the times that a cat purrs. Obviously, when we stroke the cat, the cat will purr. But if you take your cat to the veterinarian and you know that's quite a stressful situation for your kitty, they also purr at that moment, too. And so that kind of makes it not quite a pleasure response anymore. I would think maybe it's very similar to a human when we hum. We can hum when we're very happy, but also we hum when we're a little nervous and frightened to calm ourselves down. So maybe that's how a cat uses their purring.

LYDEN: Hmm. So is it a voluntary thing that the cat does? If I'm petting the cat in my lap, does it - he decides to start purring or is it an automatic reaction?

Dr. LYONS: I think it's a little bit of both, kind of like us blinking. We can obviously blink when we want to, but it's a rather autonomic procedure, too.

LYDEN: I understand that it's just in the past couple of years that scientists figured out exactly how cats purr.

Dr. LYONS: Right. Yeah. We've had to wait for certain technologies and imaging capabilities to come along. But, yeah, we have a better idea from the physiological point of view of how a cat actually purrs. And that's a response of different muscles both in the throat and in the diaphragm that allows them to make that sound. Certainly, larger cats can't make the exact same noise, but a very similar noise. So it depends on the bones in the throat, but also some of the muscle responses.

LYDEN: Now, could you tell me this? How is it that Eartha Kitt purrs?

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Dr. LYONS: You know, that I don't know.

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LYDEN: Feline geneticist Leslie Lyons of the U.C. Davis School of Veterinary Medicine, thanks very much for joining us and…

Dr. LYONS: Oh, my pleasure.

LYDEN: One other question. Your name is Leslie Lyons, do you get some ribbing about your name?

Dr. LYONS: Oh, all the time, but I'd have to say our lab is - we call it the Lyon's den and, definitely, cats are us.

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