Every so often, rare medusa's shocking couple catching waves (8)
I believe the answer is:
eardrums
'every so often rare medusa's shocking couple catching waves' is the definition.
I can't tell whether this defines the answer.
'every so often rare medusa's shocking' is the wordplay.
'every so often' indicates alternate letters.
'shocking' indicates anagramming the letters (letters shocked or shaken).
The alternating letters of 'rare' are 'rr'.
'rr'+'medusa'='rrmedusa'
'rrmedusa' anagrammed gives 'EARDRUMS'.
Can you help me to learn more?
(Other definitions for eardrums that I've seen before include "Membranes that vibrate when sound strikes them" , "Hearing membranes" , "auditors" .)