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' shows that the letters should be reversed in order.
'star' in reverse letter order is 'RATS'.
(Other definitions for rats that I've seen before include "Heels" , "Oh no" , "Blast" , "Mild oath - sewer residents" , "Damn" .)