Categories: purring

What is physically happening inside a cat when he purrs? Does the cat choose when to purr?

Cat purring in contentment. “He was purring the entire ride home” – Photo:

At one time, in the long distant past, there was a theory that the cat’s voicebox had nothing whatsoever to do with purring. Experts argued that it was to do with the cat’s blood flowing through her veins into the heart creating turbulence. The diaphragm amplified the vibrations it was thought. The theory seems fanciful today. Another theory put forward by Dr Desmond Morris in his cat encyclopaedia called Cat World refers to “The False Vocal Chord Theory“.

Dr Morris’s Theory on the Cat Purr

This theory describes purring as originating in the cat’s voicebox otherwise known as the larynx. We are told that the cat possesses a second pair of vocal chords in addition to the ordinary vocal cords. These are referred to as ‘false vocal cords’ or vestibular folds.

This second pair of chords is the secret behind the purring mechanism. The theory suggests that purring is no more than noisy breathing a bit like snoring when asleep. When the cat inhales and exhales air passes over the false vocal cords making the well-known purring sound. Dr Morris says, “air has to be interrupted by the contraction of the laryngeal muscles about 30 times a second”. See also the link below the article. Cats purr towards each other as well as towards humans.

Dr Bradshaw’s Theory on the Cat Purr

Dr John Bradshaw describes how cats purr in his book Cat Sense. This book was written much more recently and therefore relies on better knowledge. He says that the rumbling sound is produced as the vocal cords are vibrated by a special set of feline muscles. The sound is not like a hum produced by air passing over the cords but rather by the vocal cords banging together, “like an old-fashioned football rattle”. He says cats sometimes hum at the same time which reinforces the purring sound. And sometimes cats add a meow-like sound to the purr to create an added urgency to it; a high pitched variant (play the audio file below). This happens when cats are looking to be fed.

The domestic cat purrs instinctively. Therefore it is not a rational decision to purr at a certain moment. It is a natural, reflex, instinctive action as a consequence of the circumstances under which a cat finds herself. In that regard, perhaps it is a bit like a person humming to himself when he’s content or perhaps whistling. Although, we all know by now that purring does not only take place when a cat is content. For example, it can happen when a cat is about to be euthanised at a veterinarian’s clinic. I discussed the reason behind purring on another page.

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Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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  • IMHO, it depends on the cat. My Maine Coon normally trills, but when she can't find her soft mouse toy, her trill is at a much higher octave with an urgent sound to it. She settles right down when she finds her little toy and her sounds resemble a lower, barely audible purr. When she's hungry, she just taps me and then meows rather loudly to make her request understood. (Reminds me of Simon's Cat, lol.)

    My Chartreux usually squeaks when he wants something, like when he's hungry. Again, it's a higher pitched sound; otherwise, he's pretty quiet. He's also an affection junkie and a head bunter, so when he wants attention, he begins with the head bunting and when stroked, settles down to a very low pitched purr of contentment. Should you stop petting him before he's ready, he grabs your arm/hand with that frantic higher pitched sound. Pretty funny.

  • Yes, I haven't heard it a lot but cats seem to purr to self sooth when they are in pain or extremely distressed.

    I'd believe that if we could see in there somehow, we'd see a flatter portion of the wind pipe where by virtue of a slight tightening at that portion, the walls of their pipe ripple and bang into the opposing side like say, a flattened water hose. That would explain why it would easily flutter with air moving in both directions, too. That kind of thing is something that happens to us too, when we feel excited or distressed (public speaking, or when we tell a lie) and our throat tightens, huh? Cats simply developed the noise using that natural reaction.

    I've also heard the high pitched purring referred to as "trilling". It's so adorable, if I may say.

    • It's weird that with modern science we haven't yet figured out how cats purr. It's probably because there hasn't been much interest in it, like so many things about cats, the information has come slowly.

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