Borrow a quarter and a can of soda from an audience member. Let people thoroughly examine both the coin and the can to be sure they're authentic.
Have someone write her initials on the coin with a permanent marker. Wait a few seconds for the initials to dry.
Hold the can on its side, parallel to the ground. Slap the coin hard against the bottom of the can.
Pull your hand back to show that the coin is no longer there. Be sure to angle the bottom of the can slightly away from the audience because the coin will be resting just under the lip of the can's bottom.
Lift the can upright, with your fingers cupping the bottom, facing the audience. This will allow the coin to drop from the rim of the can's bottom into your palm.
Grab the can from the top with your other hand and show the audience there is nothing in the bottom.
Put the can, on its side, in the hand that holds the coin, which is now flat against the side of the can. Turn the can and slide your thumb over the coin.
Slowly push the coin up with your thumb, toward the top of the can, eventually sliding it onto the sealed opening of the can. At this point, to hide the sound of the moving coin, tell the audience that you're shaking the coin to the bottom of the can. This makes the audience focus on the bottom while you slide the coin to the top, which is angled toward you.
Open the can, keeping your fingers between the opening and the audience. This will hide the coin sitting on top. When the can opens, the coin will drop right into the mouth.
Pour out the contents of the can to reveal the initialed coin inside.