Sounded like a pig has nothing put in pen (6)
I believe the answer is:
oinked
'sounded like a pig' is the definition.
(I've seen this in another clue)
'has nothing put in pen' is the wordplay.
'has nothing' becomes 'oed' (I can't explain this - if you can you should believe this answer much more).
'put in' means one lot of letters goes inside another (instruction to solver).
'pen' becomes 'ink' (I've seen this in another clue).
'oed' placed around 'ink' is 'OINKED'.
Can you help me to learn more?
(Other definitions for oinked that I've seen before include "Sounded like pig pen" , "Made noise like cartoon pig" , "Made sound like cartoon pig" , "Grunted" , "Made a piglike noise" .)