There are many examples of foreshadowing in To Kill a Mockingbird, though Harper Lee's approach is more subtle than most writers'. One example comes when Jem and Scout receive air rifles for Christmas, and Atticus warns Jem that it's "a sin to kill a mockingbird." The innocent songbird becomes symbolic of human innocence in the novel, and Atticus's warning foreshadows Tom Robinson's own death by the prison guards' rifles when he tries to take flight. (Chapters 10, 24)
Aunt Alexandra's premonition--"somebody just walked over my grave"--in Chapter 27 foreshadows the dangers that the children encounter in the following chapter. Lee's decision to use Halloween, the spookiest of all the days of the year, as the time of the attack by Bob Ewell is magnified throughout Chapter 28. The children's walk is a "scary place": They no longer fear "Haints, Hot Steams, (and) incantations," but they don't recognize that an evil human element may be present. The bird above issues warnings of danger, and the sudden arrival of Cecil Jacobs on the way to the school foreshadows Bob's own appearance and Boo's unveiling on the way home. After the pageant, the children turn down a ride home from a purposely anonymous driver who warns the children to "be careful of haints."