Listen to them fart endlessly (4)
I believe the answer is:
hear
'listen to' is the definition.
(to hear something is to listen to it)
'them fart endlessly' is the wordplay.
'them' becomes 'he' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'endlessly' says to take the centre (the ends of the words are removed).
The middle letters of 'fart' are 'ar'.
'he'+'ar'='HEAR'
Can you help me to learn more?
(Other definitions for hear that I've seen before include "Perceive aurally" , "attend" , "Get wind of" , "Hark" , "Discover aurally" .)