What’s behind humour about girl? (6)
I believe the answer is:
retina
'what's behind humour' is the definition.
I can't judge whether this definition defines the answer.
'about girl?' is the wordplay.
'about' becomes 're' (regarding).
'girl?' becomes 'tina' (**).
're'+'tina'='RETINA'
Can you help me to learn more?
(Other definitions for retina that I've seen before include "Sensitive layer in eye" , "Light-sensitive membrane of the eyeball" , "Membrane in eye, sensitive to light" , "Light-sensitive eye lining" , "Ocular membrane" .)