To show signs of anxiety, impatience or stress

Peter's wife was having their first baby and he was in the waiting room biting his nails (to the elbow)

La moglie di Pietro stava partorendo il loro primo bambino e Pietro se ne stava in sala d'attesa mordendosi le dita (fino al gomito)

I was next for the conversation exam and I was waiting biting my nails

Ero la prossima per l'esame orale di conversazione e aspettavo il mio turno mordendomi le dita

This expression, sign of emotional tension, has been described (c. 35 B.C.) by Horace, the Roman satirist, in his Satires (Book 1):
"et in versu faciendo saepe caput scaberet, vivos et roderet ungues."
(scratching his head as he made his verses, and often biting his nails to the quick.)