Judah Schwartz, my physics professor at MIT, used to end each lecture by saying "Comments? Questions? Puzzles?" Usually there would be dead silence from the cl

Judah Schwartz, my physics professor at MIT, used to end each lecture by saying "Comments? Questions? Puzzles?" Usually there would be dead silence from the class. And then he would say "I don't believe you." And he waited for someone to ask a question.