Crossword Genius

Informant and traitor combination that's not venomous (5,5)

Ross

I believe the answer is:

grass snake

I'm a little stuck... Click here to teach me more about this clue!

'not venomous' is the definition.
I can't judge whether this defines the answer.

'informant and traitor combination' is the wordplay.
'informant' becomes 'grass' (term for an informant or traitor).
'and' is a charade indicator (letters next to each other).
'traitor combination' becomes 'snake' (I can't explain this - if you can you should believe this answer much more).
'grass'+'snake'='GRASS SNAKE'

'that's' is the link.

Can you help me to learn more?

(Another definition for grass snake that I've seen is " legless wild thing".)

I've seen this clue in The Daily Express.
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