Ham and eggs eaten up by the mouth (7)
I believe the answer is:
overact
'ham' is the definition.
(ham can mean to overact)
'up by the mouth' is the wordplay.
'up' becomes 'over'.
'by' says to put letters next to each other.
'the mouth' becomes 'act' (I can't justify this - if you can you should believe this answer much more).
'over'+'act'='OVERACT'
'and eggs eaten' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for overact that I've seen before include "Do what ham thespian does" , "Exaggerate" , "Be excessive like fulsome thespian" , "Perform with exaggeration" , "Play (part) in an exaggerated manner" .)