The main metaphor in this story is, as the first answer says, thunder. The metaphor of thunder seems to be used just to describe the sheer physical awesomeness of the dinosaur, but it is much more than that. The thunder metaphor is also used to show us how any given action can have massive ramifications that are not seen. Any action, even one so seemingly innocuous as the killing of a butterfly, can “thunder” on and change the world.
Thunder can be thought of as a prominent repercussion of a previous event. The lightning flashes, but then the thunder comes and demands our attention much more than the lightning does. If you are turned the wrong way, you don’t see the lightning, but there is no hiding from the sound of the thunder. The thunder is only a result of the lightning, but in many ways it is more conspicuous than the lightning and has more of an impact on us.
The same is true in the story. Eckles’ actions do not seem very important at all. You could easily turn away from them and not notice. But what comes next—the thunder—cannot be ignored. Eckles’ action changes the whole of modern society. A small action has had tremendous repercussions.
Thunder is truly the major metaphor of this story, but it is not just about the way the dinosaur moves. It is also a metaphor for the impacts that our actions can have on the world.
Ray Bradbury's story, "A Sound of Thunder," comes alive with vivid images and creative figurative language that creates an atmosphere of exotic and magnified life. Truly, Bradbury's figurative language immerses the reader into a rather frightening exotic world where the unexpected can easily occur.
The metaphor "sound of thunder" is used to describe the steps of the terrifying and mammoth Tyrannosaurus Rex. As it walks, the earth shakes and rumbles. When Travis, a guide, first sees it, the jungle is filled with sound: "twitterings, rustlings, murmurs, and sighs." And, then there is silence as the small animals sense the approach of a monster. "Silence. A sound of thunder." The steps of the huge dinosaur shake the earth as though thunder were rattling. Further, the sounds of the Tyrannosaurus Rex are described as "lizard thunder" as the dinosaur's great tail swings and lashes sideways. Then, when the T-Rex dies, "[T]hundering, it clutched trees, pulled them with it," and "[T]he thunder faded." This larger-than-anything creature shakes the earth with its mammoth size, creating a metaphoric thundering.