In a far-off kingdom, it is well known that the only way to counteract being poisoned is to drink a stronger poison, in order to neutralize the weaker one. Long ago, the king who ruled this kingdom wanted to ensure that he possessed the strongest poison in the kingdom, to ensure that he could counteract any attempts on his life.

So the king called the royal treasurer and the kingdom's best pharmacist. He gave each the task of concocting the strongest poison possible within one week. At the end of this week, each of the two men would drink the other's poison, followed by his own -- whoever survived, succeeded.

The pharmacist went straight to work, but the treasurer knew he had no chance -- after all, the pharmacist was far more skilled in this field. Instead, the treasurer formulated a plan to make sure he survived and the pharmacist died. At the end of the week, the pharmacist came to the same conclusion, and realized that the treasurer would use whatever underhanded means necessary to survive. So the pharmacist, too, concocted a plan to ensure his own survival.

At the end of the week, the king summoned both of them once again, and the two drank the poisons as planned: first the other's, and then their own. The treasurer died, the pharmacist survived, and the king did not get what he wanted. What happened?

The treasurer planned to drink a weak poison immediately before the trial, after which he would drink the pharmacist's stronger potion and neutralize his own. As his own poison, the treasurer brought water -- this would have no affect on him, and would ensure that the pharmacist died from his own strong poison.

The pharmacist, being clever enough to figure out the treasurer's plan, brought water as well. In the end, both drank water in the presence of the king, leaving the treasurer as the only one who had drunk any poison. The pharmacist survived, the treasurer accidentally poisoned himself ... and the king was left with two bottles of ordinary water.

Today's brain teaser courtesy of Braingle.com.