Once upon a time there was a kingdom. A king and a clown lived in this kingdom. Unfortunately they hated each other so they agreed that they will poison each other one day.
There are only twelve vials of poison in whole kingdom and they are locked in one chamber in the castle.
The poisons have numbers from 1 to 12. The higher the number the stronger the poison. Effect on human body is simple – you drink the poison, you die. Each stronger poison neutralizes all weaker poisons which means that poison 12 neutralizes all poisons, number 11 all poisons but 12 etc. (If you drink 11 and than 12 nothing happens. If you drink 12 and than 11 you die.)
The king enters the chamber with poisons first and takes all the even poisons (2, 4, 6, 8, 10, 12). Than the clown enters and takes the rest. They meet in the throne hall where each fills one cup and hands it over to the other who immediately drinks it. Now each fills the cup once again, now for himself, and drinks it (hoping to save his own life).
What did the clown do that he woke up the second morning and the king was dead?
Premises: Each of them (the king and the clown) PRIMARILY wants to survive. If he survives he wants to poison the other as surely as possible. There is one dose of each poison – it’s not possible to divide it. The poisons are fluids without color or smell and they have the same consistency as water.