Maybe you have just some ideas but not the whole answer. That's fine too.
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I'm not sure what background information you are supposed to know on this. Certainly any discord among the jurors makes tension. You need a collective jury to to hand down a verdict. These jurors are hot, tired, and upset. A group will naturally look favourably to strong evidence that will end the trial. Any discord could convince other jurors to change their mind and shift the group dynamics.
These jurors want to end the trial fast and give the judge the most obvious verdict. Which is "Guilty." However, the #8 juror opposes to the so called obvious verdict, so the others get upset and angry. This also triggers their wanting to have a reasonable answer to their discomfort. They continously show disrespect to the #8 juror redirecting the attention to some jokes and games showing their disatisfaction till the first big point is made. And it goes on shifting one by one to the otherside. However, the #8 juror started it because he only wanted to hear more about the boy's life and his circumstances. But as the conversation went on the small points made by others helped him think of ways to prove the kid "not guilty." Thats what I think.