Cats have a highly ritualized grooming sequence. First, they lick the inside of a front paw and then sweep the saliva-moistened paw first in small and then in ever-increasing circles from back to front around one ear. They then groom the other side of the face in like manner. Next, comes body grooming, limb grooming and, finally, tail grooming.
In the process of cleaning and conditioning their limbs and feet, cats may pay some attention to their nails. Cats' nails are also conditioned by their scratching hard surfaces to shuck off old nail husks. Some cats, like some people, develop the "bad" habit of constantly chewing or biting their nails for no apparent reason.
The expression "nail biting experience" goes hand-in-glove with anxiety and conflict. The same connection seems to hold true for cats, too. While cats are not normally seriously dedicated nail groomers, some do seem to bite their nails more or less continuously.
Compulsivity may explain the problem. The equation for a compulsive behavior is: Anxious personality plus anxiety-promoting circumstances = displacement [into a seemingly irrelevant behavior that is enacted repetitively] and thus the seemingly mindless performance of the behavior. The behavior then becomes ingrained, reaching "habit" proportions, and bingo, you have a compulsive disorder.
Why Cats Bite Their Nails
Displacement behaviors, and their more ingrained derivatives, compulsive disorders, arise out of conflict and other anxiety-promoting situations. You only have to look at the person next to you at the traffic lights to understand the sequence. The light is red indicating that the driver must stop. But the person wants to go. This situation represents a conflict. The result is often that people displace into grooming; grooming their hair, picking their teeth, or biting their nails. Check it out next time you're stopped at a light.
Displacement grooming is common in cats, too. Many anxious cats will take to grooming themselves in a variety of anxious situations. Often times, this grooming is directed toward the cat's coat, but sometimes it involves the cat's nails, perhaps depending on which neural pathways were most frequently activated when the cat was young.
What To Do About Nail Biting
In most cases, absolutely nothing has to be done, as the behavior itself is not intrinsically damaging. However, since it implies some anxiety, you might want to get to the root of the problem and address any ongoing causes for concern that may be plaguing your cat.