If you have ever spent any amount of time around a cat, you will have heard or felt them purr. It seems to the ultimate sign of cat happiness and contentment. Having a purring cat sitting on your knee is likely to send you off to sleep as well because it is so relaxing. But why do cats purr? And is it just a sign of happiness?
For a long time, experts weren’t even sure how a cat created the purring noise but recent tests have shown that the purr comes from the brain. The cat’s brain sends a message to the laryngeal muscles in the throat that cause them to twitch at anywhere from 25 to 150 vibrations (Hz) per second. This creates a separation of the vocal cords when they breathe in and out and makes the purring noise. Most of the time, the vibrations are at such a low pitch that we don’t even hear them but can feel them when close to the cat.
The purr isn’t just a domestic cat trait either. There are many types of wild cats and even some closely related species such as mongooses, civets and genets that can purr. Even animals as unrelated as hyenas, racoons and guinea pigs have their own version of it. With the bigger cats, the rule is if you can purr, you can’t roar. This is because the makeup of the voice box isn’t stiff enough to create the purr.
It is thought that the bigger roaring cats don’t need to purr because they are members of prides and need to be frightening and loud. Whereas the smaller cats live alone and don’t need to intimidate others with the roaring.
Why do cats purr?
While we traditionally think of purring as a sign of contentment and happiness, this isn’t always the case. Studies have shown that cats can also purr when they are frightened or feel threatened and is a bit like the human smile. Some people smile because they are happy but also when they are nervous or they want something – it is an appeasement gesture.
In fact, one study by the University of Sussex in Brighton England showed that purrs have subtle variations just like our smiles do. For one thing, cats have learned that a certain type of purr can irritate humans and they use this to persuade people to do what they want them to, usually feeding them or cleaning out their cat litter tray.
The ‘solicitation’ purr is used less when they are one-on-one with their human, as they don’t feel the need to grab the attention as much. The purr used in this situation is gentler and less grating on the ears.
The purr may also have healing properties when at the 25 Hz frequency. This may be why they purr when in pain, when giving birth or even when near death. Kittens also purr soon after being born and specialists in bioacoustics have said that the purr may be a kind of noise therapy to help them heal and feel better. It has even been found to have beneficial effects on humans at the same frequency.
No matter what the reason, the purr is almost always a lovely sound to hear. It is relaxing and reassuring that your beloved pet is happy and content to be with you. And if it is a purr designed to get you moving and achieve their aim, it will still sound nicer than a loud meow!