Crossword Genius

File that rodent wags! (8)

Ross

I believe the answer is:

ratstail

I'm a little stuck... Click here to teach me more about this clue!

'file' is the definition.
I know nothing about this answer so I can't tell whether this works.

'rodent wags' is the wordplay.
I cannot really see how this works, but
'rodent' could be 'rat' (rat is a kind of rodent) and 'rat' is found within the answer.
This explanation may well be incorrect...

'that' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.
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