Curiouser and curiouser

Lots of new books rolling in these days. In today's bunch, I lost myself for a few minutes in Professor Stewart's Cabinet of Mathematical Curiosities, by Ian (as in Professor) Stewart. It's full of little factoids, puzzles, brain teasers, and, yes, even math jokes. A taste of a few (of the sillier) items:

Q: Why did the chicken cross the Mobius band?
A: To get to the other ... um ...

Q: If five dogs dig five holes in five days, how long does it take ten dogs to dig ten holes? Assume that they all dig at the same rate all the time and all holes are the same size.
A: Five days. (Each dog digs a hole in five days.)

An engineer, a physicist, and a mathematician are staying in a hotel. The engineer wakes up and smells smoke. He goes into the hallway, sees a fire, fills the wastepaper basket from his room with water, and pours it on the fire, putting it out.
Later, the physicist wakes up and smells smoke. He goes into the hallway and sees a (second) fire. He pulls a fire hose off the wall. Having calculated the temperature of the exothermic reaction, the velocity of the flame front, the water pressure in the hose, and so on, he uses the hose to put out the fire with the minimum expenditure of energy.
Later, the mathematician wakes up and smells smoke. He goes into the hallway and sees a (third) fire. He notices the fire hose on the wall, and thinks for a moment ... Then he says, "OK, a solution exists!" - and goes back to bed.