What do you put in the back?

(1)When I was in my second year of high school in Korean,
(2)In a literary work, Duju came out, so the teacher…
(3)You all know what I’m putting in the after-week.
(4)Of course, all of them.
(5)Prince Apostle of Silla
(6)But the teacher said, “Hey, you guys! You’re putting in grain!”
(7)So, the members…
(8)I put grain in the back and started whispering. So funny.