There are several instances of foreshadowing in Bradbury's "A Sound of Thunder":
1. The title itself acts as a prediction since thunder often precedes a storm, which can be a dangerous occurrence.
2. As he enters the Time Safari, Inc. office in order to pay for his trip Eckels's nervousness is apparent as he is described in this manner: "Warm phlegm gathered in Eckels' throat; he swallowed and pushed it down." (His lack of nerve serves as a predictor of what he later does.)
3. The words of the official also foreshadow future events:
If you disobey instructions, there's a stiff penalty of another ten thousand dollars, plus possible government action, on your return.
4. Eckels's conversation with the man-behind-the-desk hints at how easily circumstances can be altered by time. After Eckels looks at the Time Machine, he remarks,
"Makes you think, If the election had gone badly yesterday, I might be here now running away from the results. Thank God Keith won. He'll make a fine President of the United States."
The man agrees, saying that the other candidate, Deutscher would have instituted a dictatorship. He adds that before the election, people called, wondering if they could go live in 1492 if Deutscher were to win. But, he adds, the company only does safaris.This foreshadows the change of time that Eckels causes, giving Deutscher the election, after all.
5. The man's warning to Eckels, "We don't want anyone going who'll panic at the first shot. Six Safari leaders were killed last year, and a dozen hunters" also foreshadows the panic that Eckels does feel when he sees the Tyrannosaurus Rex.
6. The guides' strict warning to Eckels to not stray from the Gravity Path because Time can, then, be altered certainly suggests the grave mistake of stepping on a butterfly that Eckels makes.