Sticking with twitch (3)
I believe the answer is:
tic
'twitch' is the definition.
(I know that tic is a type of twitch)
'sticking with' is the wordplay.
'with' indicates the answer is hidden within the clue.
'TIC' is hidden in the letters of 'sticking'.
(Other definitions for tic that I've seen before include "Convulsive twitch (of face)" , "Convulsion" , "Twitch in anticipation" , "Muscular contraction" , "Convulsive spasm" .)