How and why cats purr

Cecil's Columns/Staff Reports
1

Why do cats purr? Why do Cheshire cats grin?

Or, page 7 of the paperback edition of The Straight Dope (1986 edition, at least).

I’m not really so concerned with the “why” part of the question - the utility of a purring mother to a young kitten is obvious, and for the most part, “because they can” is really enough of a reason for me in most other situations when adult cats tend to purr. I find myself making similar sounds in similar situations sometimes, both of contentment and fear/pain. I see that there has been some recent studies that show that the frequency of sound of typical purring is helpful to healing - http://www.animalvoice.com/catpurrP.htm

But, I’m still having a hard time with the “how” - back in 1976, Cecil wrote “Since it’s very difficult to induce a cat to purr while you are examining his hyoid apparatus, the truth may never be known.” Well, since then, all sorts of methods of viewing the inside of a body have been developed - I’m going to avoid the obvious jokes about PET or CAT scans, but has no one ever thought to stick a purring kitty in medical imaging devices? Dope one up on catnip and/or some other kitty drug, so it’s nice and happy and sedate and won’t move, get the owner to pet it and get it purring, and slide it on in to the machine. Or do some sort of modified ultrasound on one of those hairless cats (they’ve got to be good for something). If they can “see” these tiny little tumors with modern medical machinery, can’t they figure out the source of vibrations that are so strong that a blind and deaf newborn kitten can detect?

Personally, purring is what gives cats an edge over dogs in companionship animals. But, if it really does help with healing, the interesting question becomes not so much why cats purr, but why only the feline family has developed such a useful mechanism.

2

Hi and welcome to the SDMB! :slight_smile:

Found this, FWIW.

http://www.sciencenet.org.uk/database/bio/animals/mammals/catsdogs/b00940d.html

3

Both my old dog (rest his soul) and my mom’s current dog have been known to purr when happy. They don’t use the same mechanism as cats (cat purring seems to be unique to cats), and I think they’re just doing the same thing they do to growl, but in context, it’s definitely a sign of contentedness. But then again, both dogs were raised in a household full of cats, so maybe they’re just confused.

4

Hey, thanks for the welcome. And for the link - I spent a couple days digging through the web, and found a lot of discussion on the “why”, but very little on the “how”. Those that did mention it either said that no one really knew, or that it was due to “vibrating blood vessels”. I’m sorry, but to me, that’s not much of an explanation. Blood vessels aren’t muscles, or anything else that it makes sense could produce the vibrations. I mean, yes, the blood vessels in the region where the purr can be fealt are probably vibrating, but then so is everything else. You put your hand on a cat that is purring strongly, and it is obvious that the vibrations orriginate somewhere roughly forward of the cat’s front legs. Listening to the sound, it is also obvious that there is a slight difference in the sound of the purr when the cat is inhaling vs when it is exhaling. So, for me, a reasonable explanation of the purring mechanism would have to address how the sound is related to respiration. I will take their word for it that the larger felids only have an audible purr while exhaling, as I don’t really want to get close enough to one to know for sure. The volume control has always seemed to me to be voluntary, based on personal experience. While giving a cat active affection, it will purr loudly, but if you taper off to a lesser degree of attention, the volume of the purr will slowly decrease.

BTW, I meant “in my opinion” in that last paragraph… I’m not trying to choose sides, in the interest of full disclosure, I love both dogs and cats, and almost every one I’ve met of either has loved me. In a perfect world, I’d have one of each. Alas, my cat does not like being within 20 feet of anything else that is four-legged. So no dog for me. I need a pet, for the companionship factor, and because I’m an animal lover. Dogs offer a built-in security system, but the psychological benefit of a purring cat is much more important to me. Every cat with which I am personally acquainted is just as loving and devoted to their person as the average dog - they all run to meet their person at the door when they come home, sleep near them, beg for affection and follow the people around the house. Sometimes, the pretend that the don’t care, or that they were going into that room anyway, but most usually tend to forget about doing their fabled indifference act.

I have never personally known a “purring” dog, but I’ve known people that have had them, always similar to the description given by Chronos. Dogs raised around a bunch of cats that pick up on some of the mannerisms (one friend had a dog that would try to wash its face like a cat), and all of them mentioned the dogs trying to purr. When I thought about it, I realized that I make purr-like sounds while enjoying a good stretch or massage or soak. Based on how right it feels to make these kind of sounds, I really have little problem believing that there is some sort of therapeutic benefit to expressing contentment with sonic frequencies in that general region.

Just my opinion/thoughts on the matter.

5

How on earth do you find yourself purring without doing it deliberately? I have to consciously shape my throat to make anything resembling a purring sound.