Twist or squirm (6)
I believe the answer is:
writhe
I believe this clue is a double definition.
'twist' is the first definition.
(I know that twist can be written as writhe)
'squirm' is the second definition.
(synonyms)
(Other definitions for writhe that I've seen before include "Squirm in pain" , "Move sinuously" , "Twist in agony" , "Painfully move" , "Twist as in pain" .)