Why (and How) Cats Purr

Source: Lucas Pezeta / Pexels

Cats are fickle animals. It is often difficult to know whether they love us or hate us.

Purring is one of the very few signs we can confidently take to be a clear indication of affection or at least of being at ease in our company.

But is purring something cats do to show us that they are OK with us being close to them? Is purring something they do at all?

There are two schools of thought about purring. They both have fancy names, but the general idea is straightforward.

According to the "active muscle contraction" theory, cats have some form of control over their purring: It results from potentially voluntary actions. So, it is something cats do. It is akin to speech in that sense.

The alternative is the even more scientifically sounding "myoelastic-aerodynamic" theory, which denies all this. According to the this theory, purring is unlike speech. It's more like involuntary snoring, which cats have no control over.

It is a purely physiological feature of how air stimulates the cat's larynx in a way that triggers self-sustaining low-frequency oscillations of the cat's vocal cords.

A new study uses very unusual methods to decide between these two theories. What is unusual is that this study did not use cats, at least not live cats. It used the larynges of dead cats.

The eight cats who contributed to this experiment all died peacefully, and their larynges were then removed and placed in an environment with moist air or a certain temperature. The question was whether these larynges, entirely detached not just from any intention to communicate anything but also from the very animals they once belonged to, are capable of producing the same purring sounds.

The surprising result is that each of the eight larynges (again, detached and placed in a tube of moist warm air) produced self-sustaining low-frequency oscillations. All of the eight larynges made purring sounds. Without any cats attached.

Does this experiment show that purring is a purely physiological reaction that cats don't have any control over? No. Just because these larynges produced purring sounds in and of themselves, this does not mean that your cat has no control over purring.

Nothing in this experiment excludes the possibility that your cat is purring when she is comfortable with you. What this experiment shows is that the purring sound could also be produced when nothing like that is going on.

So purring, in some ways, is neither like snoring nor like speech. It is more like raising one's eyebrows, smiling, or winking. We can raise our eyebrows to convey all kinds of communicative intentions. But sometimes, our eyebrows go up.

The same goes for purring. It can be the result of your cat feeling comfortable with you. But it can also have completely different triggers, which have nothing to do with anything heartwarming. The point is you can never be sure, which adds to the complexity of the mysteries of the feline mind.