Cheshire Puss,' [Alice] began, rather timidly, "`But I don't want to go among mad people,' Alice remarked.
Oh, you can't help that,' said the Cat: `we're all mad here. I'm mad. You're mad.'
How do you know I'm mad?' said Alice.
You must be,' said the Cat, `or you wouldn't have come here.'
Alice didn't think that proved it at all; however, she went on `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.

Author: Lewis Carroll