Which one washes his face?
Person2: The one with the dirty face washes his face.
Person2: “Very clever,” Person1 says. “Give me another test.”
Person2: We have already established that. The one with the clean face washes his face.
Person2: I didn’t think of that says Person2. It’s shocking to me that I could make an error in logic. Test me again.
Person2: Each one washes his face.
Person2: Please give me one more test.”
Person2: Neither one washes his face.
Source - http://leaches.net/moline/sermon--072.html