What impact does Swiv’s narration have on the novel? How would the novel change if narrated by Mom or Grandma?

Why does Swiv frame the story as a letter to her father? What impact does his absence have on her? What impact does it have on Mom? How would the story change if it were narrated traditionally, without the letter?

How does Mom’s pregnancy impact the events of the novel? Why does she continue to rehearse a play in which she almost certainly will not appear?