Said the animal is no fool! (6)

I believe the answer is:

mousse

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'fool' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

I can't explain the rest of the clue.

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(Other definitions for mousse that I've seen before include "Something for the hair" , "Frothy creamy substance for styling hair" , "Shock treatment" , "A dessert, or creamy substance used to style hair" , "Dish; hair preparation" .)

I've seen this clue in the Evening Standard.

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