* 3 cups
    * a napkin
    * some magical know-how

Step 2: The trick

The cups and balls trick is one that has confounded audiences for hundreds of years. The cups are laid out in a row upside down. One ball is placed on top of the middle cup. The other cups are then stacked on top. When they are lifted up, there is a ball underneath the stack! It appears that it has penetrated through the base of the cup. Another ball is placed on top, the cups are stacked again and lifted to reveal two balls. This happens one more time so that all three balls end up underneath the middle cup.

Step 3: How it’s done

Tear a tissue into four equal sized pieces. Roll each piece up into a ball.
Now line up 3 cups in a row. Place one ball of tissue in the middle cup but don’t show anyone. The trick revolves around this hidden ball so no one can know it’s there. Keep it a secret.
Line up your cups and the three remaining balls. Turn each of the cups upside down. Be careful when turning over the middle cup not to let the hidden ball fall out, or the trick will be ruined. Turn the cup quickly to avoid this.
Now that you’re ready to do the trick with one ball concealed under the middle cup, place one ball on top of the middle cup. Then stack the other two cups over it. Click your fingers and lift up the stack to reveal the ball you hid underneath the middle cup. The audience will think the ball you placed on top of the cup has travelled through the base.
Separate the cups and, again being careful not to reveal the hidden ball, turn them upside down. Put the cup containing the ball in the middle. There are now two balls underneath the middle cup but the audience believes there is only one.
Place the next ball on top of the middle cup, stack the others over it, click your fingers twice and reveal that there are now two balls under the stack. With practice, you should be able to make unstacking the cups without the ball falling out look completely natural.
Place the last ball on top and stack the others once again. Click your fingers three times and show the audience all three balls under cups.
Finally, separate the cups and line them up as they were at the start.

Done

Hundreds of years of mystery solved.