Bull's proverbial trigger (3,3)

I believe the answer is:

red rag

(Other definitions for red rag that I've seen before include "Something proverbially annoying a bull" , "It is offensive to a bull" , "Provocation to bull" , "Gerard (anag) - cause of infuriation" , "Proverbial bull enrager" .)

I've seen this clue in the Sydney Morning Herald.

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