A Cat's Purr Does Not Always Mean Contentment

Just as a wagging tail does not always indicate a happy dog, purring is not always a sign of a contented cat. Cats do purr when contented, but they also purr when they're not feeling well or when they're injured. They also often purr when they're stressed out at the vet's office. I used to have a kitty (see above pic) who purred constantly while the vet examined him, making it impossible to hear a heartbeat, and I know he wasn't a happy cat during that time!

Science is only now starting to figure out how cats do it (it seems that the brain sends signals to the laryngeal and diaphramatic muscles, causing them to vibrate), but the why is still a bit of a mystery. Some researchers speculate that the purr may have originated as a method of communication - for the mother cat and kittens to tell each other that "all is well." Many cats have figured out how to use purring as a way to communicate with their humans, and they'll often add a meow to the purr to get their way quicker. Another theory says that cats purr to help themselves relax, which would explain why they often purr when hurt or stressed.

According to WebMD Healthy Pets, some scientists believe a cat's purr can also help physical healing. A specialist in bioacoustics by the name of Elizabeth von Muggenthaler was one of the first to suggest this (you may recognize her name if you've read about the paralyzing power of the tiger's roar). The theory says that the frequency of a cat's purr (usually around 25 Hertz) increases bone density and promotes wound healing.