Take a can and remove both ends and attach a balloon that has been cut so it can fit over one side of the can tightly. Place a small amount of foil on the balloon. You can make it stick with a bit of glue.
Hold the can to your mouth and speak, scream, hum, etc. through the open end as you shine a flashlight onto the foil. The light should bounce to the wall you are standing near. As you speak the light will move.