Animals' star turn (4)
I believe the answer is:
rats
'animals'' is the definition.
(rat is a kind of animal)
'star turn' is the wordplay.
'turn' is a reversal indicator.
'star' backwards is 'RATS'.
(Other definitions for rats that I've seen before include "Heels" , "Oh no" , "Blast" , "Mild oath - sewer residents" , "Damn" .)