Check it out: http://www.hunkinsexperiments.com/pages/multiplication.htm
The website is full of fun experiments in cartoon form:
surprise people at work
push a needle through a balloon without popping it.
We used to do the last one at summer science camp, with a slightly different method. All you need is a big balloon (don't inflate it super-tight!) and a wooden skewer dipped in vegetable oil. Then just push it, very slowly, through the balloon. It's easier to go from tip to knot (the long way), at least until you get some practice!