Throughout Book One, Bigger often imagines possible action—usually violent—that he can take to relieve the anxiety and tension he feels because of his position in society. Wright uses his imagination in this regard to foreshadow actual events that take place later in the novel.
The simplest version of Bigger's predictive imagination comes early in Book 1. When he and Gus talk about how white people and racist societal structures control their lives, Bigger correctly (if vaguely) predicts his future: "I feel like something awful's going to happen to me. It's.... it's like I was going to do something I can't help." If it wasn't already obvious at that point in the novel, Wright foreshadows that Bigger will get himself into great trouble. But Bigger also points to the problem that he will struggle with for the whole novel and only come to terms with in his prison cell awaiting death: racism so completely controls Bigger's life that he cannot help what he does.
Bigger's imagination gets more specific as the book goes on. At the pool hall with his friends, Bigger imagines committing a violent act for the first time in the novel, describing what it would be like to attack Gus: "He could have taken one of the cue sticks and gripped it hard and swung at the back of Gus's head, feeling the impact of the hard wood cracking against the bottom of the skull." Both of Bigger's murders are attacks to the head: he smothers Mary's face with a pillow, and he later cuts off her head to burn it; and he bashes Bessie's head in with a brick. Bigger becomes obsessed with Mary's severed head through much of Book 2. When he imagines hitting Gus with a pool cue, he predicts how central the head will be to his violence in the rest of the book.
Bigger also imagines his new job while watching Trader Horn at the movie theater with Jack. In that imagination, he correctly predicts the problem in Mary's life that will, indirectly yet inevitably, lead to Bigger killing her: "Maybe she had a secret sweetheart and only he would know about it because he would have to drive her around; maybe she would give him money not to tell." If not for Mary's "secret sweetheart," Jan, Bigger might have been able to hold the chauffeur job with the Daltons comfortably; because Bigger agreed to "drive her around," he got gets up in Mary and Jan's drunken evening, leading to Mary's death.
Foreshadowing, in sum, is a common feature in Book 1. Native Son is a thriller, so this is a rather standard literary device. Wright uses this foreshadowing to continually ratchet up the tension and to fill the reader with anticipation and worry.
While Jack and Bigger watch Trader Horn in the movie theater, the narrative turns away from the film and goes inside Bigger's mind. Wright announces this switch from conventional narrative to a stream of consciousness: "Bigger tuned his eyes to the screen, but he did not look. He was filled with a sense of excitement about his new job." From this point on, it is clear that the narrative has turned to Bigger's thoughts. The novel is in a proximal third person: while the book has a third-person narrator, it is not omniscient, and the reader sees only what Bigger sees. So when Bigger looks away from the movie and turns to his thoughts, so goes the narrative.
Bigger's imagination goes many places as the film goes on. First, he imagines his life working for the Daltons. He thinks about living with rich white people with a "sense of excitement." He considers how he can act like them: "It was all a game and white people knew how to play it." In this moment of imagination, Bigger introduces a theme that will be important to the rest of the novel. Bigger (and, the reader assumes, Wright) sees racism as a structural fact that overrules people's lives, not as individual actions that people take. Life is a "game" and racism is just one of its rules; "white people," Bigger astutely realizes, "knew how to play it," as the hard reality of racism benefits them and hurts him.
Bigger's stream of consciousness also foreshadows later parts of Book One. At this point, Bigger has heard of Mary but knows little about her. As he imagines living with her, he makes guesses about her personality: she might be a "hot kind of girl" who "had a secret sweetheart." Bigger, of course, turns out to be exactly correct, to Mary's great misfortune. Thus, the stream of consciousness includes foreshadowing to Mary's personality and, indirectly, to the cause of her death. Bigger also, though, imagines the future incorrectly. As he thinks to himself, he criticizes himself for his behavior: "He was a fool for wanting to rob Blum's just when he was about to get a good job." But this certainly does not foreshadow his experience at his "good job." Bigger's desire to do crime and cause violence ("wanting to rob Blum's"), even if it is not his fault or guided by emotions beyond his control, certainly does not go away, even after he gets his "good job."
Then, at last, Bigger turns his attention to the movie again. He hasn't followed the plot of the film, and as he looks at the screen, the narrator remarks on "the screams of black men and women dancing free and wild, men and women who were adjusted to their soil and at home in the world." Bigger was too busy imagining his life and the racism that controls it to see the film in front of him, showing scenes of Black liberation, sovereignty, and joy. After this, Jack finally speaks again, and the narrative fully leaves Bigger's head and returns to the real world.
The furnace is a crucial image in the novel: it is the place of the climax of Book 1 and the focus of much of the investigation in Book 2. The first time Bigger encounters the furnace is very thoroughly described, thus foreshadowing its important position in the narrative.
Bigger learns of the furnace from Peggy. While she shows him around the Dalton house she tells Bigger that one of his tasks will be, occasionally, to refill the furnace with coal. Notably, the last thing that Bigger and Peggy talk about before going to the furnace room is Mary. Peggy is worried about her: "The Lord only knows where she got her wild ways." Wright puts this discussion just before the introduction of the furnace to subtly foreshadow that Mary's "wild ways"—her late-night drinking and illicit boyfriend—will lead to her death and burning in the furnace.
Peggy also takes great care to specifically describe how the furnace works. She tells Bigger that the furnace is a "self-feeder," and Wright describes the sound of "a loud rattle of fine lumps of coal sliding down a metal chute." Peggy doesn't describe anything else in the household in such detail. Bigger's main task is to drive the family around, yet Peggy glosses over the car, showing him the Buick parked in the garage and moving on. Wright foreshadows the furnace's importance through this detailed description. The reader guesses, only from this passage, that the furnace is sure to be relevant going forward.
The detailed description of the furnace, the first time it appears in the story, foreshadows the moments of great violence around it later. The specific description animates and energizes the action later in Book 1. Because Peggy told Bigger exactly how the furnace works, the reader knows exactly what Bigger has to do when he burns Mary's corpse. Thus, the foreshadowing not only works to increase the reader's expectation around the furnace, but also to make later scenes more tense and exciting.