David: I noticed that I sometimes click on the same dot twice in very fast succession. I'm aware that this is not a bug, but a problem with my hand or mouse, more likely the former. But I don't think it'd do any harm if you'd include a check for the case, so the system wouldn't register two wrong answers for the player (if he chooses wrong).

Maybe you could add this at the end of your to do list, at the place where the most unimportant things have a home.

Just thought I'd mention it.