And how do you know that you're mad? "To begin with," said the Cat, "a dog's not mad. You grant that?" I suppose so, said Alice. "Well then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore, I'm mad.

Alice's Adventures in Wonderland & Through the Looking-Glass