The rumbling noise that cats and kittens make in their throats or chests is called purring. It is commonly known as an expression of contentment. However, that is not always the case. Research has shed new light on why and how cats purr and even how it affects humans. It is more complex than a simple expression of happiness.
How Cats Purr
Until recently, how exactly cats purr was unknown. According to WebMD Pets, scientists now know that purring results from the brain telling the larynx muscles to vibrate, causing them to twitch at the rate of 25 to 150 vibrations per second, or hertz. This, in turn, causes a sudden separation of the vocal chords. Inhaling and exhaling during this process creates the sound.
Why Cats Purr
Purring tends to be associated with a relaxed, calm cat, and indeed it does accompany those moments. However, cats also purr when feeling frightened or threatened. In these situations, it is believed to be a sign of submission. Cats might also purr when they are sick or in pain. The belief about purring under those circumstances is that it is a way of comforting themselves, like a child sucking his thumb.
How Purring Affects Humans
Being the sly little beings that they are, cats can also use purring to their advantage on their humans. When they want or need something from humans, like food in their bowls while their humans are trying to sleep, they add a special vocalization to the purr. WebMD says that this sound is "an overlay of a high-frequency cry-meow." Because it is a louder, more urgent sound than the otherwise content-sounding purr humans perceive the difference and respond to it more quickly.
Who Else Purrs
The domestic cat is not the only feline purring. His larger cousins the bobcat and the mountain lion also purr. Interestingly enough, they cannot roar. Big cats who roar, such as lions and tigers, cannot purr. Further, purring is not reserved for cats alone. Other animals that purr are civets, genets, mongooses, guinea pigs, raccoons and even hyenas.