Unnerve snake, cutting its tail (6)
I believe the answer is:
rattle
'unnerve' is the definition.
(thesaurus)
'snake cutting its tail' is the wordplay.
I cannot quite see how this works, but
'snake' could be 'rat' (rat snake is a kind of snake) and 'rat' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rattle that I've seen before include "flap" , "Clatter or bang" , "Disconcert - conductor, Simon" , "American viper" , "Gurgling sound in throat" .)