Custom at Duquesne University dictated that if a professor was ten minutes late, class was canceled. One professor arrived early for a 9 a.m. lecture. He placed his hat on his desk, and went to the faculty room. Before he knew it, it was 9:10.

By the time he got back to his classroom, it was empty. The next day, he let his students have it.

"When my hat is here, " he fumed, "I'm here!" The following day, the professor arrived at 9 a.m. He was met by the sight of 28 hats on 28 desks -- and no students.