Why does a cat purr?

To think that cats purr for only one reason is a mistake, purring is a sign of characteristic joy in cats, we can hear it on several occasions, when you pet them, when they play with something they like, when they knead, even, sometimes, when you look at them, etc.  

How is this sound made?

Well, according to several scientists, although not enough studies have been carried out to rule out other explanations, it is that this sound originates in the thorax, within the wall of the vena cava where it crosses the diaphragm. The muscles compress the blood flow causing the bronchial tubes to vibrate and this relaxing sound is created.

Another theory is that noise is caused by quick tremors of the cat's larynx muscles, which dilate and restrict the glottis at high speed, making the air vibrate when inhaling and exhaling.

Why do they do it?

Kitties start purring at a very young age to communicate with their mother so that she knows where her son is. But when they are adults, they keep on making that sound to communicate with us, with other cats or with themselves.

But not only is it a distinguishing sign of enjoyment, it can also be of stress or nerves, as a way of calling someone they know when they are away or to avoid being hurt. You may have heard your cat purring at the vet and that is probably the reason, although there are many theories about it. Like that of ethologist Paul Leyhausen, who interprets it as a sign that the purring cat is communicating that it is not a threat.

There are known cases in which they have purred when they were injured or dying, we imagine that it is again for the same objective, to communicate with someone asking, perhaps, for help. Cats have also been seen giving birth while purring, either to ask for help or to calm down.

The cat's purring releases sensitive endorphins that, according to studies, whole body vibrations of 35 to 50Hz could help stimulate bone healing, thus demonstrating that the frequencies of this purring could help kittens keep their skeletons healthy.

Alba Serrano, Dog and Cat Psychologist and Master's Degree in Clinical Ethology from the UAB, @enlamentedelosanimales.