Animal disturbed when a gun goes off (3)

I believe the answer is:

gnu

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'animal' is the definition.
(type of antelope)

'disturbed when a gun goes off' is the wordplay.
'gun' can be anagrammed to 'GNU'.
Though, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for gnu that I've seen before include "Wildebeest" , "Large heavy antelope" , "hitherto unknown, we hear" , "Animal" , "Literally wild beast" .)

I've seen this clue in the Evening Standard.

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