Remove the cap from your pen.
Insert the end of your elastic tape into the pointed end of the pen cap. You may need to fold and twist the tape to work it into the hole. Continue feeding tape into the pen cap until the tape extends out of the opposite end.
Pull a small amount of the elastic tape out of the pen cap and tie a simple overhand knot at the end of the tape. Pull the elastic tape and knot back into the pen cap. Give the tap a few good tugs to lock the knot into place.
Replace the pen cap on the pen.
Use a clothespin to attach the opposite end of the elastic tape to the inside of a jacket, just between your shoulder blades.
Put on the jacket and pull the pen around your side. Remove the cap and show the audience the pen, making sure to hide the elastic tape behind your hand.
Replace the pen cap, hold the pen in both fists and then release. The elastic tape will pull the pen back into your jacket, leaving your hands magically empty.