Snakes like empty pockets (4)
I believe the answer is:
asps
'snakes' is the definition.
(asp is a kind of snake)
'like empty pockets' is the wordplay.
'like' becomes 'as'.
'empty' means to remove the middle letters.
'pockets' with its middle removed is 'ps'.
'as'+'ps'='ASPS'
(Other definitions for asps that I've seen before include "poisonous things" , "Poisonous creepers" , "Poisonous snakes" , "Cleopatra's cobras" , "Small vipers" .)