"This year she had the extra joy of showing it to her small brother, and of terrifying him as well as herself. When they had done this many times they came back to the house to tell everybody that they had done it. He boasted. She mocked. They squabbled."
How does Julia feel about her little brother? Does she love him? Hate him? Find him an annoyance? Be sure you read what is IMPLIED by their reactions to each other.