The mystery surrounding why cats purr has fascinated pet owners for many years. There is no definitive answer as to why cats purr, but there are a few theories that have been suggested. The effect on humans is usually soothing, but one thing is clear – cats don't always purr because their happy.

The purr of domestic cats is unique, although other felids like bobcats, cheetahs, and pumas also purr. Kittens learn to purr within their first few days of life, even before they open their eyes, and a mother often purrs while delivering her babies. Cats also purr when they are hurting, scared, or...