Crossword Genius

Snakebite: a possible answer to this question in pub! (5,4,6)

Ross

I believe the answer is:

whats your poison

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

'answer to this question in pub' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'snakebite a possible' is the wordplay.
I cannot quite understand how this works, but
'a' is within the answer.
'possible' could be 'on' ('not on' can mean unacceptable or not possible) and 'on' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for whats your poison that I've seen before include "A question that may be asked at the bar" , "Local offer" .)

I've seen this clue in The Telegraph.
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