Forms of nail-biting.. biting fingernails. Biting fingernails legs. Non-biting fingernails

Forms of nail-biting:
1) biting fingernails, even if short. This can lead to deformities or injuries fingers. 

2) biting fingernails legs when a few of them, which refers to the synergy of my body. 

3) non-biting fingernails: either as a joke or a genuine desire to have them take advantage of an opportunity for young children to practice their hobby.