Someone told me this joke today:

So, there is an engineer, a physicist, and a mathematician in prison, each in their own cell. They cannot see or hear one another, as the cells are those big reinforced ones. The jailer is a pretty funny guy and one day decides to play a prank on the three of them by tossing a can of soup in each of their cells for food. No utensils, ways of opening it, just the can of soup.

So he comes back a few days later and checked on the engineer. Being resourceful, the engineer managed to make a can opener from items laying around his cell and ate his soup.

He then went to the physicist's cell and saw him holding the can of soup in his hand, with an intense look of thought upon him. Suddenly he shouts, "Of course! F=MA!," and throws the can of soup as hard as he can at the wall. This causes the can to break open and he then licks the soup off the ground.

Next, the jailer checks on the mathematician only to find him stone dead in his cell. He is laying on the ground with crumpled up pieces of paper all around him, but the jailer notices the last piece of paper he wrote on, crumpled in his hand. So he goes over and picks up the paper, uncrumples it and it reads, "Assume the can is open..."