Creeps furtively to sort out snakes (6)
I believe the answer is:
sneaks
'creeps furtively' is the definition.
(I've seen this in another clue)
'sort out snakes' is the wordplay.
'sort out' indicates anagramming the letters.
'snakes' anagrammed gives 'SNEAKS'.
'to' is the link.
(Other definitions for sneaks that I've seen before include "Moves craftily" , "In school slang, tells tales" , "Informers" .)