Anyone who has interacted with a cat — or even read about one for that matter — knows that cats purr.
Some cats purr more than others. Most people think cats purr because they are happy; although this is one reason, it’s not the only one.
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The most confusing thing about purring, however, occurs when the cat is asleep. Although most people don’t ever hear purring while their cat is asleep, many claim they do.
How Do Cats Purr?
Experts are still trying to determine how exactly it is that cats purr, but most agree that it originates in the brain.
They think cats have a repetitive neural oscillator that tells their laryngeal muscles to twitch, usually at between 25 and 150 vibrations a second (Hz). When this vibration occurs, the vocal cords separate, which creates the famous sound.
If you think your cat has purred for minutes or hours straight, you might be right. It’s possible because purring involves both inhaling and exhaling, allowing cats to breathe during the process.
Why Do They Purr?
If you do something to make your cat very happy, such as give her a favorite toy, pet her or cuddle (depending on the cat), she will probably start purring. Some cats even purr while eating, and this might be because they are contented at mealtimes. But, again, happiness is not the only reason cats will purr.
Some cats will also purr when they are upset or when one of their family members is upset. This may be a calming method to help them (or their fellow cats or humans) relax. If that’s the case, it seems to work as cats have been associated with a great deal of relaxation in humans.
You will also notice that cats purr when they are sick or scared. Once again, this may be a calming method — or it’s maybe it’s similar to when humans smile at an enemy.
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Let’s go back to that initial question: What about purring when cats are asleep?
Veterinarians seem to still be split on this issue. Some say that cats can indeed purr in their sleep, while disagree. The most common theory is that cats can purr when they are in light sleep, but once they reach deep sleep, the purring stops.
The thing to remember, however, is that cats spend most of their resting time in light sleep. This is an evolutionary advantage from their time as wild cats before they were domesticated. That means your cat may be sleeping for several hours and still purring, but this is because she hasn’t reached deep sleep yet.
This video shows a pet parent awoken by his sleeping kitty’s purring:
Why Would They Purr in Their Sleep?
We know the reasons cats purr in general, and some of those reasons can also explain why your cat purrs in her sleep.
The most common explanation is that the cat is purring for some reason (most likely contentment) while falling asleep and simply is continuing the process as she enters light sleep. It’s a continuing reaction.
But consider another reason: The vibrations may be a way to stimulate bones and muscles without using up a great deal of energy. Therefore, it makes sense that the process continues in sleep, because it is not related to any conscious thought.