Shook when flustered (7)
I believe the answer is:
rattled
I believe this clue is a double definition.
'shook' is the first definition.
(rattling is a kind of shaking)
'flustered' is the second definition.
(I know that flustered can be written as rattled)
'when' acts as a link.
(Other definitions for rattled that I've seen before include "Made a series of clattering sounds" , "what pit viper did" , "Extremely disconcerted" , "Shaken" , "Hot and bothered, perturbed" .)