When packing, hurt, stifles a cry of pain (7)
I believe the answer is:
stowing
'when packing' is the definition.
'stowing' can be an answer for 'packing' (stowing is a kind of packing). I am unsure of the 'when' bit.
'hurt stifles a cry of pain' is the wordplay.
'hurt' becomes 'sting' (if something stings, it hurts).
'stifles' means one lot of letters goes inside another.
'a cry of pain' becomes 'ow' (exclamation of pain).
'sting' placed around 'ow' is 'STOWING'.
Can you help me to learn more?
(Another definition for stowing that I've seen is " Packing or storing away".)