Getting the hackles up, which is frightening? (4-7)
I believe the answer is:
hair-raising
'frightening?' is the definition.
(I've seen this in another clue)
'getting the hackles up which is' is the wordplay.
I cannot really see how this works, but
'is' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hair-raising that I've seen before include "Very scary" , "Very frightening" , "Extremely alarming" .)