In a cinema during a performance one of the audience gets up, makes his way along the row of seats and goes out into the foyer.
A few minutes later he returns and asks the man sitting at the head of the row:

"Excuse me, was it your foot I stepped on when I was going out a moment ago?"
" Yes, but it doesn't really matter. It didn't hurt at all."
"Oh, no, it isn't that. I only want to make sure that this is my row."