"Overheen" means "across". You can drop 'heen' in this sentence. :)
Can you hightlight both parts of the verb, please? That way we know it is together.
In this case the verb is rennen. What is separate is the proposition overheen.
mmm weird sentence. Does this mean the mouse is runing "on top of" the cheese? As it seems to be valid both across and over I can't get a clear picture of what the mouse is doing. Any suggestions?
I think of "across" the cheese as; the mouse is off the cheese then (gets on the cheese) runs "across" it, then gets off the cheese.
Whereas runs "on top of" the cheese, could mean the mouse runs on the cheese and potentially stays on the cheese.
I hope I am right and I hope this helps.