True story. I live in the US. A [famous] colleague of mine was invited to give a lecture at a major German university in front of a professor's class. At the end of his lecture, the professor picked a random student out of the class, and the student came down and gave a perfect 1-minute summary of the lecture.

My colleague asked how the students could be so disciplined. The professor said it was simple: they knew he would pick one at random, so they all had pre-prepared summaries of the lecture based on studying my colleague's submitted lecture notes the day before.