Could it be better ?

An engineer, a chemist, a mathematician, a topologist, a physicist and a theoretical physicist are sent to prison and given only a can with food. Then they are left alone for a week.After a week the guards check the cells.The enigneer is quite OK and you can see a broken can in the corner. When he was left alone and hungry he took out a lever and broke the lid of the can.Also the chemist is alife and in the corner of his cell you can see the steaming left-overs of a can. When he was left alone and hungry he took out some acid and etched away the lid of the can.The mathematician however is no longer. On the wall you can see the following words: I define the can is open. Conclusion, you cannot eat from an open can!