Riddle: The King and the Poison
I realized that I have been deficient in the Riddle department. Here is one that I came across recently on Usenet:
The King and the Poison
In a far away land, it was known that if you drank poison, the only way to save yourself was to drink a stronger poison, which neutralizes the weaker poison.
The King that ruled the land wanted to make sure that he possessed the strongest poison in the kingdom, in order to ensure his survival in any situation. So the King called the royal Pharmacist and the royal Scribe, and he gave them each one week to make the strongest possible poison. At the end of the week, each would drink the other's poison, then his own, and the one that survived would be the one that had created the stronger poison.
The Pharmacist went straight to work, but the Scribe knew that he had no chance, for the Pharmacist was much more experienced in this field. So instead, the Scribe created a plan to survive and make sure that the Pharmacist died. On the last day, the Pharmacist suddenly realized that the Scribe would know that he had no chance, so he must have a plan. After a little thought, the Pharmacist realized what the Scribe's plan must be, and he concocted a counter plan to make sure that he survived and the Scribe died.
When the time came, the King summoned both of them. They drank the poisons as planned, and the Scribe died, the Pharmacist survived, and the King didn't get what he wanted.
What exactly happened?
Don't Google it. 
Give it a shot on your own. Come on, think it through.
The Scribe's plan was to drink a weak poison PRIOR to the meeting with the King.
Then he would drink the Pharmacist's strong poison, which would neutralize the weak poison. As his own poison he would bring water, which will have no affect on him, but the Pharmacist who would drink the water and then his poison, would surely die.
When the Pharmacist figured out this plan, he decided to bring water as well. So the Scribe who drank poison earlier, drank the Pharmacist's water, then his own water, and died of the poison he drank earlier. The Pharmacist would drink only water, so nothing will happen to him. And because both of them brought the King water, he didn't get a strong poison like he wanted.