Gin perhaps beginning to sting mouths (5)
I believe the answer is:
traps
'mouths' is the definition.
(I know this)
'gin perhaps beginning to sting' is the wordplay.
'gin perhaps' becomes 'trap' (gin is a kind of trap).
'beginning to' says to take the initial letters.
The first letter of 'sting' is 's'.
'trap'+'s'='TRAPS'
(Other definitions for traps that I've seen before include "Devices to catch, animals say" , "Corners" , "gins" , "used by jazz drummers?" , "Pony carts; ensnares" .)