Shake up (6)
I believe the answer is:
rattle
'shake up' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rattle that I've seen before include "Venomous creature's warning" , "Fluster" , "Child's toy; unsettle" , "Shake - baby's toy" , "Baby's toy - conductor" .)