Why do cats Purr? Cats (big and small) are the only animals who purr. Contrary to popular belief, purring isn't speaking. The purr comes from two membrane folds, called false vocal cords, that are situated in the larynx behind the actual vocal cords. Cats purr 26 cycles per second, the same as an idling diesel engine. Cats purr both when inhaling and exhaling, keeping the mouth completely closed. Scientists believe purring is produced by blood in a large vein in the chest cavity that vibrates and is then magnified by air in the windpipe. Kittens are born blind and deaf, but the vibrations of their mother's purring is a physical signal that the kittens can feel. It acts as a homing device, signaling them to nurse. Kittens begin purring at about one week old; then it's a signal to the mother cat that they're getting their milk and are content. Since purring is non-vocal, it doesn't interfere with the suckling. Contrary to another popular belief, cats don't purr purely for pleasure. Be alert: a deep purr can indicate that a cat is in pain or distress. Female cats will purr when in labor. Cats may purr in fear or anxiety. They will also purr in anticipation of being fed or stroked. Big African cats only purr in short bursts, but the house cat can purr for hours. Curiously, scientists tell us that a cat never purrs when alone.