Shock waves? (4)
I believe the answer is:
perm
This clue might be a double definition.
'shock' is the first definition.
The definition and answer can be both related to bodily activities as well as being verbs in their base form.
Perhaps you can see an association between them that I don't see?
'waves?' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for perm that I've seen before include "Old-fashioned haircut" , "Hair setting treatment; pools selection system" , "Football pools forecast - wavy hairdo" , "make waves" , "Possibility in pool" .)