Will he have you laughing in a shake? (3)

I believe the answer is:

wag

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'a shake?' is the definition.
(I know that shake can be written as wag)

I don't understand the remainder of the clue.

(Other definitions for wag that I've seen before include "Brisk rear movement or funny fellow" , "Comedian" , "Jocular person" , "Move briskly to and fro" , "Wave to and fro, as a dog's tail" .)

I've seen this clue in the Evening Standard.

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