Answer: The man must first place a coin in the center of the table. He then must replicate every move the serial killer makes on the opposite side of the table. Eventually the serial killer will run out of places to place a coin and the man will win.
Answer: The prisoner grabbed one of the marbles from the jar and concealed it in his hand. He then swallowed it, and picked up the other marble and showed everyone. The marble was black, and since the other marble was swallowed, it was assumed to be the blue one. So the mean king had to set him free.