Those in that film about ants? (4)
I believe the answer is:
them
'those in' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'film about ants?' is the wordplay.
'film' becomes 'm' (Fritz Lang film).
'about' says to put letters next to each other.
'ants?' becomes 'the' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'm' after 'the' is 'THEM'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for them that I've seen before include "Let -- eat cake" , "Certainly not us, the other lot" , "(To/from) those people" , "people objectively" , "... in another case, they" .)