Here's the way bonuses work as far as I've been able to figure it.
First bonus: you get a piece when you score over 100. Second bonus: you get a piece when you score over 200. Third bonus: etc.
It would be much better if simply going over a square meant you collected/landed on whatever was there.
It is loads more fun if you try to speed through the level and ignore score.
I don't understand why there need to be two squares, why they are changing colors, and why we get so many points per click. Some concrete goal other than making them as small as you can would be nice. A slightly less jarring background color would be nice, too.
Of someone put lemon juice on the wall, the smart thing to do would be to use heat to see if it contains a message. So I go to my inventory, and find that you cant actually use any of the items...Now I refuse to complete this game.