I was at the continuation high school today. Math class. The students do all their work on computers. They access their textbook and work through the problems at their own pace. The program has animated examples, so the students pretty much work on their own all period.
My job was to assist when the students got stuck (sometimes they had a hard time understanding the examples) and to check off the assignments on their sheets when they finished. They had to get at least 70% correct on each before they got credit. Many managed to get through two or three sections during class.
The computers were set up along the three walls of the class. The front wall was where the teacher's desk was. When the students were working, their backs were to the front of class, so I could see what was on their computers, but they would have to turn around to see me.
One student raised her hand. I checked off her assignment; she got 100%, so I initialed her paper. Two students over, one boy was having a conversation that was inappropriate for class.
I wasn't really listening. All I heard was the F-bomb. So, I called him on it. And I shocked him.
"Man, you've got ninja skills."
He didn't realize that I was right behind him. He hadn't heard me. And I guess he didn't feel me behind him.
I played like I heard the entire conversation (it was more fun that way), and I reminded him that he shouldn't be saying such things in class. (I couldn't really pull the "get to work" bit that I usually pull as he was on task at that moment. His side conversation was more of a random comment.) Then I walked away.
It's fun to catch students off guard like that. It happens to me a lot. They'll say something and then realize that I heard every word. Their reactions are priceless.