It’s much the same reason that we hug and kiss and chimpanzees pick fleas off each other. This is grooming behaviour that has become associated with bonding and affection. Cats and dogs don’t have hands, so their primary way of interacting with the world is by using their mouth. When they are born, the sensation of their mother licking them all over is virtually their first experience. Cats can spend between 30 and 50 per cent of their day licking themselves to stay clean. When your pet licks you, you are being given the animal equivalent of a friendly hug. They probably wonder why we don’t lick them back and insist on stroking them instead!