Jelle Bakker made a Surprise Box for marbles (be sure to check out his You Tube channel.) I thought it was really cool, so I decided to make my own out of K’nex. (I am even making one for marbles!) Here’s how it works: First, a ball enters through the top, but doesn’t exit out of the bottom. Then a second ball enters through the top, hits a bell, and then exits out the bottom. When a third ball enters in through the top, surprise! It exits out the side along with the first ball. Below are some pictures and the video. Note: I filmed and took pictures of the Surprise Box while it was attached to my upcoming ball machine. Click Continue Reading to see the pictures.