The girls are about to float alcohol in a bathtub when they realize that they're about to do something stupid. They decide to use a sake bottle to make a sensei, which is like a bottle with a handle on it. The sensei tells them how to make the sensei work, and the girls try to figure out what's going on. They're not sure what to do with the sake bottle, but they figure out that it's unstable, so they can't let it go. They figure out a way to lower the mirror in the water so that it won't float. They also figure out how to use dry erase markers, which are like markers that contain a "release agent" that keeps the ink separated from the surface of the water. The girls wonder why they didn't go to the train station to get their summer vacation off. They don't have summer vacation because teachers have to work all the time during the school year. They wonder why she's talking like that in front of the students' bottled milk, which makes them want to drink even more.