1. Cut off the bottom of the straight cup to make it an empty tube with clear ends. Cut off the neck of the balloon and cover one end of the cup. Grab the sides of the balloon and tighten it with a rubber band (like a drumhead).
2. Use glue to attach the CD to the tight balloon drum surface so that the mirror faces outward.
3. Turn on the laser pointer and shine it on the mirror. You will see a light spot reflected from the mirror to the wall. If the light spots on the wall are not clear enough, you can use a piece of stiff white paper as a screen.
4. Place the cup on the table, use books, etc. as support to fix it, and adjust the appropriate angle of the flashlight, mirror and light spot. You shout or sing from the other end of the straight cup while watching the dots of light on the wall. Hooray, the light spot started to shake and "jumped into dance".