The most obvious foreshadowing is when Travis warns Eckles about leaving the path. He states that even if Eckles stepped on and killed a mouse it could result in mice dying out, which in turn could effect other animals who rely on mice for food. Billions could be destroyed by the killing of just one animal.
However, there are more subtle hints littered throughout the story. At the very beginning, the reader can detect the nervous disposition of the main character Eckles when the author states that "Warm liquid gathered in Eckels' throat. He swallowed and pushed it down." Eckles than gives an indication of the danger of the situation he's putting himself in by saying, "Don't I get some kind of document promising that I will come back alive?" The reply by the office, "we promise nothing," is equally ominous.
In fact, the entire end of the story is summarized in the first page. First, the official says that Eckles would face government action if he doesn't follow his guide's orders, and...
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