Today I had the same class as yesterday. (The teacher's wife went into labor on Thursday. He might be out for a few days.)
I didn't mention it yesterday, but besides criminalistics, this teacher teaches physics. Since each high school only has one physics teacher, and that teacher only has a couple periods of physics, I rarely get to sub for them. This is a treat for me.
Today, all classes had a short quiz. It was 10 questions long and multiple choice. It took them roughly five minutes to finish.
I glanced over the quiz, just to see if I knew the material. I did. But it wasn't until I collected all the quizzes and got them started on the rest of their assignment that I got a chance to really look at the quiz. I wouldn't have, but one of the students mentioned something. She asked if Mr. M. had given them a trick question.
I read the question and laughed. He had. He had given them a trick question.
I didn't write it down, so I'm paraphrasing, but the gist is the same: "A person walks 5 miles east, then 3 miles west. After returning to the starting point, what is the person's total displacement?"
Get it? After returning to the STARTING POINT! Displacement? Zero.
I said that that was just like the old joke: "If a plane crashes on the border between the US and Mexico, where would you bury the survivors?"
Another girl didn't get it, but the first girl explained. Then she explained the quiz's trick question. The second girl had gotten it wrong. Then someone said that the whole class was going to be upset when they got their quizzes back. Mr. M. shouldn't have tricked them like that.
The next period had the same quiz. This time, as I was sorting answer sheets from quizzes, I noticed the answers to that question. 75% of the class got it wrong.
I thought about mentioning this to the class, but then I decided against. If they didn't notice it, I wasn't going to bring it to their attention.