Muse about creatures (4)
I believe the answer is:
emus
'creatures' is the definition.
(emu is a kind of creature)
'muse about' is the wordplay.
'about' is an anagram indicator.
'muse' with letters rearranged gives 'EMUS'.
(Other definitions for emus that I've seen before include "Aussie birds" , "Running birds" , "Muse about flightless Australian birds" , "Large flightless birds of Australia" , "laboratory units" .)