Question: You come to a cross road and see a man with two heads. A sign tells you that one head always tells the truth and the other one always lies. The sign also tells you that one road leads to life and posterity while the other leads to certain death. Now the hard part. You can only ask ONE head ONE question. What do you ask? Which road do you take? Hint: One head knows what the other will tell you.
Answer: You ask, "Which road would the other head say." You then take the opposite road. Explanation. If you happened to ask the truth teller he would tell you that the liar would say the wrong road. Therefore you would take the opposite road. If you happened to ask the liar which one the truth teller would say he would lie and say the wrong road. You then would take the opposite road.