Stand up and look angry (7)
I believe the answer is:
I believe this is a double definition.
'stand up' is the first definition.
(bristling is a kind of standing up)
'look angry' is the second definition.
(I've seen this before)
'and' is the link.
(Other definitions for bristle that I've seen before include "React in an offended way", "Stand up", "rise up", "Get angry", "React angrily".)