Snakes in pass wriggling (4)
I believe the answer is:
asps
'snakes' is the definition.
(asp is a kind of snake)
'pass wriggling' is the wordplay.
'wriggling' indicates anagramming the letters (letters wriggle or move about).
'pass' anagrammed gives 'ASPS'.
'in' is the link.
(Other definitions for asps that I've seen before include "Cleopatra's cobras" , "Pass among snakes" , "Pass around the snakes" , "Poisonous creatures" , "Small vipers" .)