An an experiment, an engineer, a physicist, and a topologist are each locked in a room with a can of food but no can opener: all they have is pencil and paper.
The next day, the engineer's pencil and paper are unused, and the walls are covered with dents. The engineer is sitting on the floor eating from the open can: he threw it against the walls until it cracked open.
The physicist's paper is covered with formulas, there is one dent in the wall, and the physicist is eating too. He calculated exactly how to throw the can against the wall so it would crack open the first time.
When they open the topologist's room, the paper and walls are covered with formulas, the can is still closed, and the topologist has disappeared. There are strange noises coming from inside the can. Someone gets a can opener and opens it. The topologist pops out and says "Thanks guys!" and adds somewhat sheepishly "I got one of the signs wrong".
A Native American woman wants desperately to have a son, so she asks her tribe's shaman if there is something she can do to make sure she has a son instead of a daughter. He gives her a buffalo hide and tells her always to sleep on it. Another woman has the same request. He gives her an elk hide and tells her always to sleep on it.
A third woman has the same request. At this point the shaman has run low on hides, but he finds an old hippopotamus hide and gives it to the woman.
Nine months later the first two women give birth to sons, and the third gives birth to twin sons. There is much amazement over the twins and the people ask the shaman to explain this wonderful occurrence. He tells them that all shamans know that "the sons of the hippopotamus hide are always equal to the sum of the sons of the other two hides."