They hear corny things (4)
I believe the answer is:
ears
This clue is a double definition.
'they hear' is the first definition.
'corny things' is the second definition.
(an ear can refer to a piece of corn)
(Other definitions for ears that I've seen before include "Organs of hearing" , "Sear (anag.)" , "Spikes (of cereals)" , "Organs for 7 down" , "Heads of corn" .)