I taught an English Literature class last semester. The class met once a week for a three hour session of lecture and discussion.
One night, a little over half-way through the term, a student who I did not recognize approached me during a break in the session. She asked me if I was, indeed, Professor XXXX and then stated: "I think I'm in your class. I've been going to the class across the hall all semester by mistake. They were talking about poetry and stuff too, so I thought I was in the right class. Did I miss anything?"