Where this isn’t from and the kind of animal it isn’t (6,3)
I believe the answer is:
guinea pig
'where this isn't from and' is the definition.
The definition suggests a singular noun which matches the answer.
'kind of animal it isn't' is the wordplay.
'kind of animal' becomes 'guinea'.
'it isn't' becomes 'pig' (I can't explain this - if you can you should give a lot more credence to this answer).
'guinea'+'pig'='GUINEA-PIG'
'the' is the link.
Can you help me to learn more?
(Other definitions for guinea pig that I've seen before include "Experimented-on animal" , "Person used as the subject of an experiment" , "One who tries out" , "Subject of trial" , "one used for experimentation" .)