Foreshadowing refers to a technique by which writers give advance hints about key plot points which will emerge later on within the story. Bradbury's "A Sound of Thunder" follows Eckels, a time traveller, as he goes back into the Cretaceous to hunt a dinosaur only to inadvertently rewrite human history.

This short story begins in the future society which the time travelers themselves come from (and which will later be recreated as a result of Eckels's actions in the distant past). At this point in the story, Bradbury provides several details that will become important later on. Even the story's first paragraph does much to set up the transformations to come. The story begins with Eckels staring at a sign. It reads:

TIME SAFARI, INC.
SAFARIS TO ANY YEAR IN THE PAST.
YOU NAME THE ANIMAL.
WE TAKE YOU THERE.
YOU SHOOT IT.

Later, we learn about recent election results and how one candidate, Keith, defeated his opponent, Deutscher. Eckels is a supporter of Keith's, and a Time Safari Employee describes Deutscher as an authoritarian, stating:

If Deutscher had gotten in, we'd have the worst kind of dictatorship. There's an anti-everything man for you, a militarist, anti-Christ, anti-human, anti-intellectual.

These details might seem incidental at first until Eckels returns from his time in the past. In that moment, their full importance within the narrative becomes clear. By describing the world as it had been, Bradbury can contrast it with the world Eckels creates. The sign we observe in the story's beginning returns, but now it reads:

TYME SEFARI INC.
SEFARIS TU ANY YEER EN THE PAST.
YU NAIM THE ANIMALL.
WEE TAEK YU THAIR.
YU SHOOT ITT.

The world has changed in other ways as well, with the election results having reversed (with Deutscher defeating Keith). Meanwhile, the Time Safari employee who had previously been a critic of Deutscher is now described as a supporter instead. Bradbury writes:

The man behind the desk laughed. "You joking? You know damn well. Deutscher, of course! Who else? Not that damn weakling Keith. We got an iron man now, a man with guts, by God!

Additionally, note how the mechanism by which Eckels rewrites history is established ahead of time by Bradbury through a conversation between Eckels and Travis. Here, Travis describes the potentially catastrophic consequences of killing a single mouse and the ripple effects that could result from apparently insignificant changes. As Travis insists:

The stamp of your foot, on one mouse, could start an earthquake, the effects of which could shake our Earth and destinies down through Time, to their very foundations.

What Travis is warning about is precisely what occurs later in the story. Eckels, panicked by his encounter with the Tyrannosaurus, inadvertently steps on a butterfly. From that change, all of history is rewritten.

Foreshadowing is a literary device that writers use to drop hints about what is going to occur within a particular story.  

Ray Bradbury's "A Sound of Thunder" is full of foreshadowing. Early in the story, the characters discuss how glad they are that Keith won the election. They briefly discuss what the ramifications might have been like if Deutscher had won the election. That discussion foreshadows the end of the story. Eckels's mistake changes the election results.  

The following exchange is also a good example of foreshadowing in the story.

"A Tyrannosaurus Rex. The Tyrant Lizard, the most incredible monster in history. Sign this  release. Anything happens to you, we're not responsible. Those dinosaurs are hungry." 

Eckels flushed angrily. "Trying to scare me!" 

At this point in the story, Eckels is full of confidence in himself. He comes off as brash and cocky; however, Eckels becomes completely terrified the moment that he sees the dinosaur.  

Once the group of hunters is in the past, I feel that there is one more significant piece of foreshadowing. The safari leaders specifically emphasize the importance of staying on the path.

"Stay on the Path. Don't go off it. I repeat. Don't go off. For any reason!"

Unfortunately, Eckels's fear gets the better of him, and without realizing what he is doing, he steps off of the path, kills a butterfly, and changes the results of the election.

Foreshadowing is an effective literary device to lend a narrative verisimilitude because it provides narrative clues that suggest events that have yet to occur. In the beginning of Ray Bradbury's science-fiction short story, "A Sound of Thunder," there is foreshadowing of the devastating mishap which occurs. Here are examples:

• When Eckels first arrives at the Time Safari, Inc., he ponders the concept of the Time Machine, and how different he would feel this day if the presidential election had been won by Deutshcer instead. He recalls how people had said if he won they would want to go live in 1492. Later, in the Time Machine, the guides caution Eckels not to stray from the gravity path. However, Eckels steps off the gravity path and a butterfly sticks to his shoe Thus, he changes the future; as he returns to the Time Safari office, Eckels notices that Deutshcer has become president and signs are incomprehensible.

• As they all travel back to the time of dinosaurs so that Eckels can shoot a Tyrannosaurus rex, the guides caution Eckels,

"We don't want anyone who panics at the first shot...six safari leaders were killed in the past."

Eckels does panic and endangers the guides, but they are able to shoot the correct dinosaur

Foreshadowing is a literary term used extensively by writers that introduces verbal and/or dramatic hints about what will occur later in the story. In science fiction master Ray Bradbury's "A Sound of Thunder," a group of hunters travel back in the past to kill a Tyrannosaurus Rex--the greatest of all dinosaurs. The hunters must follow certain rules and restrictions--specifically, they must not stray from the designated path and kill indiscriminately, for the most simple act can cause a change in the flow of history. However, one of the hunters does just that, and when the men return to the present, they notice changes in people, language and even architectural design. Most noticeably, the recent presidential election results have been reversed. Nearly all of these changes and their possible repercussions, were foreshadowed earlier in the story.