Facial twitch (3)
I believe the answer is:
tic
'facial twitch' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tic that I've seen before include "Regular muscular twitch" , "Twitch in anticipation" , "Nervous movement" , "Facial muscle spasm" , "Convulsive twitching" .)