Crossword Genius

"Traitor" Assange rethinks taking a new approach (5,2,3,5)

Ross

I believe the answer is:

snake in the grass

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

'assange rethinks taking a new approach' is the wordplay.
'assange rethinks' anagrams to 'SNAKE IN THE GRASS'.
However, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for snake in the grass that I've seen before include "unsuspected danger" , "one shouldn't meet with one on the Emerald Isle?" , "Treacherous person" , "Hidden danger" , "nasty person who turns out to be traitor" .)

I've seen this clue in The Independent.
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