Animal entering that is put out (5)
I believe the answer is:
irate
'put out' is the definition.
(I've seen this in another clue)
'animal entering that is' is the wordplay.
'animal' becomes 'rat' (rat is a kind of animal).
'entering' is an insertion indicator.
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'rat' going inside 'ie' is 'IRATE'.
(Other definitions for irate that I've seen before include "Hacked off" , "Angry - furious" , "Aggrieved" , "raging" , "I tear away, being annoyed" .)