A mathematician, a physicist and an engineer were being interviewed. As part of the process, they were given 2 brass ball bearings, left alone for a while, then asked what they had done. An engineer, a physicist, and a mathematician were on a train heading north, and had just crossed the border into Scotland.
Some Scottish sheep are black.
The mathematician looked irritated. There is at least one field, containing at least one sheep, of which at least one side is black. The chemist licked it, and put it in water to try to dissolve it. The physicist tried to break it open to get at the marrow. The engineer took it, hit the other two over the head, and ate them.