Blowgun

-A regular sized straw, that doesn't bend
-Some of those pin/needles with the small colored balls on the end
-A spool of thread

You simply tie three of four 1/2 inch or so, strands of thread around the end of the pin, so that the colored ball keeps it from sliding off. Then you just insert your improvised darts into the end of the straw and blow. Very simple concept, and lots of fun in the classroom