But why do cats purr? Biologist’s pet owners and even philosophers have debated this for centuries. Still, the exact mechanics and meaning of a cat's purr have remained shrouded in mystery.

The most common theory about cat purring is that it's produced by the vibration of "false vocal chords," or the movement of blood in the cat's chest. As to why the feline species acquired the habit of purring, the reasons probably have a lot to do with mother cat-kitten communications. Biologists believe that kittens rely on the vibrations of their mother's purr to locate her during nursing. In turn, kittens purr themselves to reassure their mother that they are doing well.

As adults, cats often purr when they are getting fed or brushed, or other good things are happening to them. However, some pet owners make the mistake of assuming that if their cat is purring, she must be happy and healthy.

Unfortunately, this is not always the case, since cats have been known to purr even when things are far from ideal. A cat who is cornered by an attacker will sometimes purr, as will a feline suffering from a terminal illness. Some experts theorize that cats purr in these situations to reduce their own level of anxiety.