In the other foot there's a corn (3)
I believe the answer is:
ear
'a corn' is the definition.
(an ear is a piece of corn)
'in the other foot there's' is the wordplay.
'in' indicates putting letters inside.
'foot' suggests the final letters (in a down clue, the bottom letter).
'there's' becomes 'a' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The last letters of 'the other' are 'er'.
'er' going around 'a' is 'EAR'.
Can you help me to learn more?
(Other definitions for ear that I've seen before include "Lend one and listen" , "organ with drum" , "Attention; seed head" , "Sensory organ" , "Bit of corn" .)