Twitch, regularly observed? (3)

I believe the answer is:

tic

'twitch' is the definition.
(I know that tic is a type of twitch)

I can't explain the rest of the clue.

(Other definitions for tic that I've seen before include "Muscle twitch" , "Localised habitual twitch, especially to the face" , "Convulsive twitch (of face)" , "jerk" , "Facial movement" .)

I've seen this clue in The Times.

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