Bradbury uses foreshadowing to build suspense and hint at the story's conclusion, planting subtle clues that relationships and characters are not what they seem.
Early in the story, Smith prods Braling to admit that his marriage has been "awful," referencing how Braling's wife manipulated him into marrying her. Smith tells the story:
"It's got around, anyway, here and there, how she got you to marry her. That time back in 1979 when you were going to Rio --"
"Dear Rio. I never did see it after all my plans."
"And how she tore her clothes and rumpled her hair and threatened to call the police unless you married her."
This surprisingly dark story of faking sexual assault interrupts the seemingly banal street scene. The story establishes a foundation of deception in the Braling marriage, which foreshadows the later twists of the story.
Braling's own language also hints at danger. When Smith jokes that Braling must have used sleeping powder to escape his wife, Braling ominously replies, "No, that would be unethical. You'll see soon enough." At the time, the comment seems flippant. But in hindsight, it subtly warns the reader that Braling has made an ethically dubious choice.
The most powerful example of foreshadowing comes through Braling Two himself. Though designed to be obedient, Braling Two exhibits early signs of emotional complexity. "Your wife is rather nice," he says to Braling early in the story. "I've grown rather fond of her." These quiet remarks hint at Braling Two's developing autonomy and romantic attachment which will ultimately drive his rebellion.