The teacher is shocked to find that the students have managed to get into his classroom through the back door. He is sure that they are "full of yang energy" and will live a long time. The teacher asks the students if they have brought a fish tank, and the students say yes. Before class begins, the teacher tells the students to knock on the fish tank and to wake up the students who are still asleep. The students do so, but the teacher refuses to wake them up. He says that he is not responsible for waking them up, and that he should not have woken them up