this is a great little catapult to annoy people with.
all you need is
paper( this will be the ammo )
first, crumple up the paper to make a little ball. you now have ammo. (sorry for the fuzzy pic)
now for the catapult. take the pen cap and put a piece of tape on the back, folding the sides in. next,take a longer piece and pot one corner on the left tape thing, then fold it around the other sides.