I'd like to recall that there's an expression along the lines of "coin dropping down" used to described the moment when an explainee finally reaches the verge of grasping a concept after the explainer tediously has gone through the pains of presenting a multitude of examples, approaches and pedagogical tricks.
Googling it gave me no hits and searching on SO for "coin" resulted in way too many. None of that was of relevance, though.
Can I use the following phrase in correct English to describe that I'm trying to explain a bit more because I see that the subject is about to get the "aha moment"?
I was about to give up but I felt that the coin was about to drop down.