Riddle: The Caterpillar believes that he and the Lizard are both mad.
Who is mad, the Caterpillar, the Lizard or both?
Answer: Answer: If the Caterpillar were sane, it would be false that he and the Lizard were both mad. Hence, if the Caterpillar were sane he would not have made the false statement. Therefore, the Caterpillar must be mad. Since he is mad, his belief is wrong, so it is not true that both are mad. So the other one (the Lizard) must be sane. Therefore, the Caterpillar is mad and the Lizard is sane.