Just give your logic
You've been sentenced to death in an obscure foreign country which has a strange law. Before the sentence is carried out, two papers -- one with "LIFE" written on it and one with "DEATH" written on it -- are folded up and placed in a hat. You are permitted to pick out one of the papers (without looking), and if you choose
the one with "LIFE" written on it, you are set free. Otherwise, the death sentence is carried out. On this occasion, a mean-spirited acquaintance of yours, bent on your demise, has substituted the paper with "LIFE" written on it with another one with "DEATH" written on it. This person gleefully informs you of what he has done and that you are doomed to die. You are not permitted to speak to anyone about this misdeed, nor will you have a chance to switch the papers or the hat yourself in time. How will you avoid certain death?

Ans:
After you draw one of the papers, swallow it. The jailer will be forced to check the remaining paper to determine what the one you drew said. The jailer will of course see a paper with "DEATH" written on it, assume you drew the one with "LIFE" written on it, and set you free.