What did Bruno discover on the other side of the fence as he was exploring in "The Boy in the Striped Pajamas"?

In
chapter 10, Bruno walks along the massive fence for the better part of an hour before he
discovers a small boy sitting by himself near the fence with a forlorn expression upon his
fence. As Bruno approaches the boy, he notices that the boy is wearing the same striped pajamas
as everyone else on the...