This is my first instructable, so if it sucks, go cry somewhere that won't develop a water spot. Just kidding!
This is really simple and super cheap.
Step 1: Supplies
all you need:
plastic bendy straw
tape or glue
Sorry for the bad pictures. My camera is crazy.
Step 2: Roll and tape
roll and tape the paper tightly. then cut off the bendy tip of the straw. tape the straw on the paper, then stick a skewer in the paper. then stick a skewer THROUGH the front of the paper.
Step 3: Last step
the final step is to add a rubber band to the front skewer. the rubber band should be about 4 to 6 inches long. if not just make sure you can pull it back about 5 inches behind the straw. place another skewer in the straw to where about 5 inches stick out the back. YOU HAVE TO GET THE RUBBER BAND EXACTLY ON THE BACK OF THE SKEWER TO MAKE IT FIRE. fire it like a sling shot. it may take practice but you'll get it. BE CAREFUL, believe it or not, it WILL pierce the skin and/or put a hole in the wall.