Two people--I dunno, could be two guys or two gals, or...whatever--walk into a bar. The first one orders H2O. The second one orders H2O, too, and dies. (If you don't geddit, ask me.)

An infinite number of mathematicians walks in to a bar. The first one orders a beer. The second one orders 1/2 a beer. The third one orders 1/4th of a beer. The fourth one orders 1/8th of a beer. Before the fifth one can order, the barkeep says, "You are all a bunch of idiots!" and he pours out two beers.

Both of these courtesy of "I Fucking Love Science."

Saul