It's silly to put a cat where a pig ought to be (6)

I believe the answer is:

scatty

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'it's silly' is the definition.
(scatty means silly or absent-minded)

I don't understand the rest of the clue.

(Other definitions for scatty that I've seen before include "Disorganised, unpredictable" , "Informally crazy or feather-headed" , "Slangily crazy or scatterbrained" , "Empty-headed" , "Feather-brained" .)

I've seen this clue in the Evening Standard.

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