A cat’s purr is probably one of my most favorite sounds. Henry, my big sweet tabby has a very deep, growling purr while Mr. Tiny Arthur has a very light and soft purr. Either way, it’s music to my ears, I can’t get enough of it.

But, what exactly causes that sign of happiness? Physiologically, how do cats purr?

While looking for information on how cats purr, one item was found conclusive across the board – that scientists and vets alike aren’t 100% sure exactly how felines make that noise. There are agreed theories on what is mechanically happening when that soft rumble occurs, but for some reason they aren’t able to prove it beyond a shadow of a doubt. I kind of like that. Cats are always thought to be a bit of a mysterious creature, so I think it’s appropriate that this also is a mystery.

So, let’s take a look at what we do know. A cat’s voice box is created by muscles called the laryngeal muscles. When a cat needs to purr, its brain will send a signal to these muscles telling them to vibrate. Unlike other noises like a cat’s meow, growl, or hiss, which happen when a cat is exhaling, purring occurs during the entire breathing cycle (an inhale and an exhale). These two actions combined send a stream of air through the vocal cords resulting in, you guess it…purrrrrr.  However, it’s also possible that a small, flexible bone in the cat’s neck called the hyoid bone is responsible. When air is pushed through your cat’s voice box, it causes the bone to vibrate, resulting in, ah yes…puurrrrrr. But wait, I’m not done yet.  You see, another theory is that the purr is caused by rapid twitching of the muscles in the larynx in which a buzzing hum is produced from from the air vibrations.

All three theories are similar enough to probably indicate that purring has to do with vibration, which, I’ll buy.

Even though we associate the purr with a happy kitty (and felines are the only animal who produce such a sound to indicate happiness), purring is actually a signal indicating other issues as well. Cats can purr when they are severely injured or close to death, most likely to expand their rib cage to help alleviate internal pain. In addition, it’s possible that purring releases endorphins, which can help the same way they help a human, to ease discomfort. Mothers who are giving birth to a litter purr through their labor, as well as when their babies are nursing. Reciprocally, the kittens use the sound to bond with their mother.

So, knowing that the purr isn’t necessarily an indication of happiness (although, let’s be honest, that’s how we like to think of it, I’m not trying to piss on your parade here), is a cat’s happy purr produced differently from its stressed purr? Folks, what we have here is the first official Raise-A-Paw that asks back!

(Image: RobynAnderson)

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