Open a wood box and remove six blocks, all different colors, and each with a hole in the middle (like a Lifesaver). Place the blocks back into the box, and secure them by running a long pin through their centers and through the ends of the box. The blocks are now locked into place. Let a spectator choose one of the colors, and you can choose another. At your command, when you open the box and tip it over, ONLY THE TWO CHOSEN COLOR BLOCKS fall out- the others stay locked in place!
And yes- if you can put blocks into a box, you can do the trick! Incredible!
THIS VIDEO DEMO IS FROM THE MANUFACTURER: