This habit of biting nails is known as onychophagia in scientific circles. For humans, various reasons are given and nervousness among them tops the list. This comes under the category of compulsive disorders:
If someone has an anxious personality and he/she finds himself/herself in circumstances which stimulate anxiety, the behavior of the person changes; it becomes irrelevant and mindless. In some cases, this irrelevant behavior continues and becomes a habit.
Cats and their habits:
It has been found that the cats love to groom themselves. If one tried to observe, it would not be difficult to notice how a cat begins with licking its paws and then comes to the grooming of other parts of the body. Normally, body grooming, limb grooming follow and in the end comes the turn of the tail.
Relatively intelligent cats (well, I didn’t know how to describe cats who don’t develop the habit of nail-biting!) shuck off their nails by scratching hard surfaces. But there are others who develop the habit of constantly biting their nails. And it is still not certain, why they develop this habit!
So, where do nails fit in?
This is because of displacement grooming. This kind of behavior arises when a person is put in conflicting situations. For example, you can notice yourself when you are approaching a light signal on the road, and the light turns red but you badly want to go on. You may find yourself biting your nails or picking your teeth or grooming your hair etc. This is displacement grooming.
Displacement grooming is common among cats. When cats find themselves in similar situations, they tend to groom themselves. In most of the cases, cats groom their coat but in some cases, they can turn to their nails. It all depends upon the psyche of your cat!
Is there a way to undo it, if a cat has already developed the habit?
Like all habits, it would be difficult and a time consuming procedure and of course, the cat needs to be cooperative! Experts say this behavior is not damaging to a cat in any way, so if one wants, one can leave the things as they are. But if you are among one who desperately want to have your cat quit this habit, then the first thing that you ought to do is to address the root problem i.e. why your cat becomes anxious and other questions. A vet can be consulted in these cases and once the problem has been identified, the next step would be to work on the root cause.