How does the author use foreshadowing in The Things a Brother Knows?

Each homecoming for Boaz foreshadows deterioration in his mental state. The once engaging and glib brother seems to have less and less to say every time he comes home. Sometimes when the family knew that he was on leave, he didn't even come home or call. Levi is most concerned about his parents and grandfather, affectionately known as Dov. They worry about Boaz and cannot wait to see him. Amanda, Levi's mother, worries the most. She has been cleaning non-stop since Boaz left hoping to be distracted from her fears.