other humans, as a way of cleaning them from the dust that accumulates on them in a very water-scarce region. Humans use licking for a number of other purposes. For example, licking can moisten the adhesive surfaces of stamps or envelopes. Many people lick a fingertip (usually the one of the index finger) for some extra grip when turning a page, taking a sheet of paper from the top of a pile or opening a plastic bag. In sewing, thread ends are commonly wet by licking to make the fibres stick together and thus make threading them through the eye of a needle easier. Another practice considered uncivilized is licking one's hand and using it to groom one's hair. Humans also use their tongues for sexual purposes, such as during cunnilingus, anilingus, foot licking, and whilst French kissing, where two people lick each other's tongues. Abnormal licking Self-licking can sometimes become abnormally frequent occasionally resulting in a lick granuloma. The most common cause of lick granuloma appears to be psychological, related to stress, anxiety, separation anxiety, boredom, or compulsiveness. Lick granulomae are especially seen in active dogs left alone for long periods of time. One theory is that excessive licking causes endorphin release, which reduces pain and makes the dog feel temporarily euphoric. This provides the animal with positive feedback from the licking, and subsequent addiction to the behaviour. Animals in captivity sometimes develop a licking stereotypy during which surfaces (walls, bars, gates, etc.) are repeatedly licked for no apparent reason. This has been observed in captive giraffes and camels. Gallery References External links Grooming in cats Hummingbird Licking Behavior Mice Licking Responses to Sweeteners The Stages of Canine Labor When Your Dog Gives Birth Video of a giraffe licking a wall Eating behaviors Ethology Saliva Tongue Hygiene Animal communication Mating