THE CAT LADY

We know it has something to do with air flow and muscle contractions in the larynx and diaphragm, but we can't be exactly sure of what's going on and, more importantly, why.

Cats purr when they feel happy or content, but they also purr when they're hungry, stressed or in pain. In fact, some cats have been known to purr just before dying, and kittens purr when they nurse. Some behaviorists believe purring is a signal to other cats that they're not looking for a fight.

So how do you know if your cat's purr is the happy kind? Look at all her other physical signals. A cat purring with a relaxed body and partially closed eyes is content. If her body is tense, it's more likely the purring is an attempt to comfort herself.

It may also mean she's attempting to heal herself. Cats purr in the range of 25 to 150 Hertz, a frequency that has been shown in medical studies to improve bone density and promote healing.