When you sing (yodel, scream, hog call, etc) into the can, the sound waves vibrate the balloon diaphragm causing the laser beam to be reflected in relation to the sound produced. Surprisingly varied patterns emerge with different vocalizations.
The can is open at both ends, with the bottom covered with a stretched balloon. A piece of Mylar is glued to the balloon diaphragm to provide a reflective surface. A laser is pointed at the center of the Mylar.
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