Show anger, as when you hit a snag (5)

I believe the answer is:

snarl

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'snag' is the definition.
(thesaurus)

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

(Other definitions for snarl that I've seen before include "Growl viciously" , "Entangle wool - show displeasure" , "Tangle; growl" , "Growl with bared teeth" , "Say something aggressively" .)

I've seen this clue in the Evening Standard.

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