Animal's expression of affirmation (3-3)
I believe the answer is:
aye-aye
'animal's expression' is the definition.
'aye aye' can be an answer for 'expression' (I have seen 'expression of agreement' mean 'aye aye' so perhaps 'expression' could also mean 'aye aye'). I'm unsure of the 'animal's' bit.
'affirmation' is the wordplay.
I cannot really understand how this works, but
'affirmation' could be 'yea' (yea is a kind of affirmation) and 'yea' is found in the answer.
The remaining letters 'aye' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for aye-aye that I've seen before include "1 across" , "Yes, skipper!" , "Rare Madagascan primate" , "Naval response to an order" , "Madagascan lemur-like primate" .)