They're Titans, After All (だって巨人だもの Datte Kyojinda Mono?) is the 6th chapter of the 1st volume and the 6th chapter overall of the Attack on Titan: Junior High manga, written and illustrated by Saki Nakagawa.
Class 4 are told they will be going on a trip to observe several classes in the Titan section of the school. While everyone is impressed with how much more advanced the Titan classes are, Eren remains skeptical. During the lunch period, all the Titans surround the students and end up stealing their lunches. Eren vows to make the Titans pay for taking food from them.
Class 4 learns from their teacher they will be going on a trip to observe some Titan classes the following day. While everyone else discusses and learns what group they are going to be with, Armin admits that he is interested as well but wonders if they will be safe during the trip.
After arriving, the class discovers that the Titan building is segmented into five different areas to accommodate the various sizes of the Titans. Armin and Jean notice Eren setting up a display of fireworks; Mikasa immediately goes over and destroys it, citing that it is both dangerous and illegal to do. The first class they observe is a math class, but are puzzled on how to get through the giant door. Mikasa and Sasha notice a smaller door nearby and they all go through it; while observing the class, they notice one of the Titans is asleep. Noticing this as well is the instructor, who throws a piece of chalk into the Titan's eye.
As they arrive to the next class, a music class, Eren reveals a recorder and vows to a skeptical Armin and Mikasa that the Titans will be amazed by his playing. They notice the Titans are performing at a higher level than expected and are all impressed, causing Eren to run away in embarrassment. Class 4 marvels at how advanced each of the Titan instructors are in comparison of their own; Eren ponders that due to the principal being a Titan as well, it could all be a facade to try and fool them. Armin then realizes the forest they are currently in is where the Titans have lunch and they are all immediately surrounded. As they try to escape, one grabs Armin but only takes his lunch. Eren recalls how the same thing happened to him during the first day of school. As the other students mourn the loss of their food, Eren vows to never forgive the Titans for this and swears to make them pay.