This riddle has been around for some time on internet platforms such as Instagram, Facebook, and WhatsApp, and many people still argue over what the answer might be, as there are many possibilities. The correct answer is The prisoner grabbed one of the marbles from the jar, 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.