rightatrium:

The Chvostek sign is a classic sign of hypocalcemia. It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped at the angle of the jaw, the facial muscles on the same side of the face will contract momentarily (typically a twitch of the nose or lips).

Chvostek’s sign may also be present in hypomagnesemia, frequently seen in alcoholics, persons with diarrhea, and patients taking diuretics.