How is it possible for bruno and shmuel to have fun together and maintain their friendship in the midst of their circumstances

I read this  book a while ago. A sad book and sad ending, indeed. It was lovely.
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Imagine you are Bruno. You are REALLY bored, have nothing to do except study. No friends, and he wants entertainment. When he finds Shmuel, it is the BEST thing that has happened. A miracle!! He instantly becomes friends with Shmuel, and by that, Bruno and Shmuel both have fun together because they are lonely.
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Now imagine you are Shmuel. Stuck in a prison. A prison where you get tortured and beaten up at least twice a day. Oatmeal with ants and bumblebees and dirt. Only a T-shirt (black and white) during the cold times. So boring. So terrifying. Yet no entertainment and no friends to escape to. But yet... he finds Bruno There were kids his age on the other side of the fence!! He instantly becomes friends with Bruno, and because they both long for companionship and entertainment, they both have fun together, although they are separated by a fence.
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Hope I helped!!
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Any more questions, ask away!!