Long hair at trial tidied up (3-4)

I believe the answer is:

rat-tail

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'long hair' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Perhaps there's an association between them I don't understand?

'at trial tidied up' is the wordplay.
'tidied up' indicates anagramming the letters.
'at'+'trial'='attrial'
'attrial' with letters rearranged gives 'RAT-TAIL'.

Can you help me to learn more?

I've seen this clue in The Independent.

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