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Before the show, each contestant is asked more than 50 personal questions in a polygraph test. Then during the show, he or she is asked 21 of those same questions, this time in front of spouses, relatives and friends, that increase in sensitivity with each question. Each question answered honestly (meaning the answer given during the show matches the answer given in the pre-show polygraph test) earns the contestant money. Answering all 21 questions honestly nets the contestant the $500,000 grand prize. Wikipedia