Fluster half of venomous reptiles (6)
I believe the answer is:
rattle
'fluster' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rattle that I've seen before include "Vibrate noisily" , "flap" , "led to Tweedledum and Tweedledees quarrel?" , "Toy for baby or football fan" , "Clatter or bang" .)