Too high-key, to blurry in spots, and too sharpened in others. Makes it look more like an autopsy shot that an entry of artistic merit. And the more chewed nails I see in this competition, it makes me feel that it's the _action_ that's the habit, not the result.
This close-up of a finger doesn't show nail biting in a new or interesting way. It isn't a visually pleasing photograph which is the most important factor in meeting a challenge.
It certainly is a habit - apparently a very popular one considering the number of entries of a similar vein. Unfortunately I don't see much more than that - nothing reaches out and says "wow."