The girl's in trousers getting the cats (8)

I believe the answer is:

panthers

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'the cats' is the definition.
(panther is a kind of cat)

'the girl's in trousers getting' is the wordplay.
'the girl' becomes 'her'.
'in' is an insertion indicator.
'trousers getting' becomes 'pants' (I can't justify this - if you can you should believe this answer much more).
'her' going inside 'pants' is 'PANTHERS'.

Can you help me to learn more?

(Other definitions for panthers that I've seen before include "American big cats" , "These felines can net harps, strangely" .)

I've seen this clue in The Telegraph.

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