Pass out, seeing serpents (4)
I believe the answer is:
asps
'serpents' is the definition.
(asp is a kind of serpent)
'pass out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'pass' with letters rearranged gives 'ASPS'.
'seeing' is the link.
(Other definitions for asps that I've seen before include "people" , "native Africans?" , "Poplars" , "because of their venom?" , "Cleopatra's cobras" .)