Never back, never back!... People don’t like going back, even if they must. I don’t like going back! And I’m not people! But I look back, sometimes, every so often, just to make sure I’m not leaving anything important behind. Like my tail! I can never be sure when I leave my tail behind me by mistake.
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 it's tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad.