Snack for rats or "rats!" (6)

I believe the answer is:

crumbs

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'rats' is the definition.
('crumb' can be a synonym of 'rat')

I can't explain the rest of the clue.

(Other definitions for crumbs that I've seen before include "Morsels of bread" , "not much of a bloomer!" , "Tiny bits of bread - golly!" , "Surprised expression; bread fragments" , "Crikey, cripes" .)

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

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