Start ruffling up the animal outside (3)
I believe the answer is:
fur
'start' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for fur that I've seen before include "Hard water pipe coating" , "Eg, sable or mink" , "Hide" , "I may fly" , "Outer skin of animal with hair attached" .)