When Bruno puts on the camp uniform Shmuel brings him, he and his friend suddenly look almost identical. The situational irony in this passage highlights the frailty of the imaginary distinctions the Nazis imposed during the Holocaust:
It was quite extraordinary. If it wasn't for the fact that Bruno was nowhere near as skinny as the boys on his side of the fence, and not quite so pale either, it would have been difficult to tell them apart. It was almost (Shmuel thought) as if they were all exactly the same really.
The situational irony in this passage shows the artificial and cruel distinction that the Auschwitz uniform represents. Bruno and Shmuel look very different when Bruno is in his street clothes. Bruno is a healthy weight, whereas Shmuel and his fellow prisoners are being starved and worked to death inside the camp. In comparison to Bruno’s clean, high-quality clothes, Shmuel’s dirty, weathered “striped pajamas” make him look dingy and woebegone. However, when both boys wear the camp uniforms, they appear nearly identical, despite leading drastically different lives. This visual similarity that Shmuel and Bruno both suddenly see exposes the absurdity of the prejudice and divisions that Nazi ideology enforced. The similarities between the boys here show how baseless the imagined hierarchies among people groups really were.
The phrase "almost (Shmuel thought) as if they were all exactly the same really" deepens the irony. The word "almost"—as Boyne uses it here— highlights the artificiality of the differences between Bruno and Shmuel. Concentration camp uniforms were intended to strip their wearers of individuality and humanity. However, the uniform actually unites the boys visually in this instance, making their similarities even clearer to Shmuel than they were already.