bite one's nails
Exhibit signs of anxiety, impatience, or nervousness, as in We'll be biting our nails till the jury comes back. Biting one's fingernails is a time-honored sign of emotional tension. The Roman satirist Horace described it about 35 b.c.: "As he wrought his verse he would often ... gnaw his nails to the quick" ( Satires, Book 1).