In this video, the instructor shows us how to make a pen gun. You will need a pen with a cap, and a rubber band. First, take the cap off of the pen and unscrew the bottom so you are left with the outer shell and the ink. Next you take a piece of tape and tape the rubber band to the outer shell of the pen, about half way down. Next, take the ink part of the pen and put it into the pen shell. Pull the rubber band back and it will fire the ink tube out of the pen.