Go quietly as a rattlesnake (5)

I believe the answer is:

sneak

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'go quietly' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for sneak that I've seen before include "thief" , "Move furtively - informer" , "Telltale; furtive person" , "Underhanded tell-tale" , "Snitcher" .)

I've seen this clue in The Globe and Mail.

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