Picture reason for dropping coffee? (3,4)

I believe the answer is:

mug shot

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'picture' is the definition.
(mug shot is a kind of picture)

I don't understand how the remainder of the clue works.

(Other definitions for mug shot that I've seen before include "police will want this from him" , "Police photo" , "Passport photograph?" , "Photograph taken for police records" .)

I've seen this clue in The Times.

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