They don't lounge in the tub on Saturday nights or spend their paychecks on expensive shampoos, but cats -- and to a lesser degree, dogs -- love being clean. Several times each day, they lick and rub their coats, removing dirt and loose hairs until their fur is clean and shiny.

Some pets, however, take cleanliness a little too far. They will lick, rub, or bite their coats for hours at a time. Sometimes they get so absorbed in grooming that they lose interest in all the other fun things in life, like eating or going for walks. The constant licking can result in bare spots in the fur, and the skin may even get raw and sore.

This condition, as well as such things as endless tail-chasing, is known as an obsessive-compulsive disorder, says Nicholas Dodman, B.V.M.S. (bachelor of veterinary medical surgery, the Scottish equivalent of D.V.M.), director of the animal behavior clinic at Tufts University School of Veterinary Medicine in North Grafton, Massachusetts, and author of The Dog Who Loved Too Much. "Sensitive, anxious, and nervous pets seem more likely to develop obsessive-compulsive disorders," he says. "And if you breed a dog with this condition, her offspring have a better-than-average chance of also having it."