You are holding a clear plastic cup.
Take a handkerchief and stuff into the cup.
Cover the cup with another handkerchief and say some magic words.
Yank the handkerchief away from the cup, and the one inside has changed color!
Pull the handkerchief out of the cup. The cup is now empty.
Stuff the handkerchief back into the cup.
And once again cover the cup with another handkerchief.
Reveal the cup, and all see that the handkerchief is back to its original color.
The secret lies in a mirror, or piece of cardboard with aluminum foil glued on both sides.
The mirror should fit snugly in the middle of the cup.
It should look like this.
The cup is ready and you can hide a handkerchief on one side.
Before performing the trick before an audience, have an assistant help you determine where to stand so the secret of the cup is not revealed. It is also important to find the right pose. When showing the cup, cover the top and bottom and tilt the cup slightly forward.
In front of the audience, you stuff the second handkerchief into the empty side of the cup. While the cup is covered by the third handkerchief, inconspicuously turn the cup so the other side faces the audience.