Massaging round, um, narrow body part, staring curiously (13)
I believe the answer is:
rubbernecking
'staring curiously' is the definition.
('rubberneck' can be a synonym of 'stare curiously')
'massaging round um narrow body part' is the wordplay.
'massaging' becomes 'rubbing' (I can't explain this - if you can you should believe this answer much more).
'round' indicates putting letters inside.
'um' becomes 'er' (both said to fill in hesitation when speaking).
'narrow body part' becomes 'neck' (necks are usually narrow).
'er'+'neck'='erneck'
'rubbing' going around 'erneck' is 'RUBBERNECKING'.
Can you help me to learn more?
(Other definitions for rubbernecking that I've seen before include "Nosily watching" , "Gaping like a tourist" , "Stupidly looking at" , "Gawping" .)