There was a huge wire fence that ran along the length of the house and turned in at the top, extending further along in either direction, further than [Gretel] could possibly see. (4.162)
Through Gretel's eyes, we see how the two sides of Auschwitz are literally separated—on one side is Bruno and his family, and on the other side is the camp and its prisoners, all of whom have no freedom whatsoever.
"[…] when we were told we couldn't live in our house we had to move to a different part of Cracow, where the soldiers built a big wall and my mother and father and my brother and I all had to live in one room." (12.704)
Shmuel recounts what happened to him and his family before coming to live in Auschwitz. Because they were "told" they couldn't live somewhere, we know that they're not free, and when they live in one room, it's just the beginning of their entrapment.
"There were too many of us in the carriages for one thing. And there was no air to breathe. And it smelled awful." (12.713)
Shmuel and his family, like many Jews, were forced to ride in train cars, packed to capacity for days. There's a lack of space, a feeling of claustrophobia, and a general disregard for the hygiene. The Nazis were terrible every step of the way.
"But don't you ever wake up in the morning and feel like wearing something different? There must be something else in your wardrobe." (14.884)
Oh, Bruno. Talk about living under a rock—for the entire span of the novel he thinks that what Shmuel and the others wear are pajamas and not prison uniforms. Of course, we can't blame him entirely; neither Gretel nor his parents explain to him about the clothes.
There, sitting at the table, a long way from the other side of the fence, was Shmuel. (15.985)
Holy smokes, Shmuel's in Bruno's house. This is the first of two times that Shmuel and Bruno are in the same space, and both instances lead to disastrous results. In this case, Shmuel gets in trouble for talking to Bruno and eating—things any person should be able to do.
[…] there was something about the people from there that made [Bruno] think they shouldn't be here in his house. (15.988)
We're kind of surprised that Bruno thinks this after all the time he's spent hanging out with Shmuel. Is it a demonstration of some inner racism he has, or just an observation he makes due to how Shmuel looks compared to his family?
"It's only food." (15.1013)
Food is only food if you never have to worry about eating. The thing Bruno doesn't understand is that the prisoners don't have the freedom to buy their own food, cook, or go shopping. They have to eat what is given to them, and usually it isn't close to enough.
In another corner [Bruno] could see more soldiers standing around and laughing and looking down the barrels of their guns, aiming them in random directions, but not firing them. (19.1278)
At this point in the novel, Bruno has crossed over to the other side. For the first time he sees what really goes on in the camp, and he quickly becomes very uncomfortable. Umm, yeah, we would, too, if we saw a bunch of Nazis walking around with guns…
[…] they were all piling into a long room that was surprisingly warm and must have been very securely built because no rain was getting in anywhere. In fact it felt completely airtight. (19.1303)
This is the second time that Bruno and Shmuel are in a room together, and unfortunately, it will also be the last. Unknowingly, they're led into a gas chamber, pushed up against many others, completely trapped, confined, and beaten.
[…] the door at the front was suddenly closed and a loud metallic sound rang through from the outside. (19.1311)
By incorporating the sound that the door makes as it's closed, we get an even deeper sense of Bruno and Shmuel's entrapment. We know that there is no way Bruno, Shmuel, or anyone else in the chamber will survive what comes next.