Beginning with the ominous Time Safari Inc. warning--"We guarantee nothing except the dinosaurs"--everything about the premise of Ray Bradbury's "A Sound of Thunder" adds to the natural suspense of the story. Going back to the past in the Time Machine, hunting a runaway Tyrannosaurus Rex, being warned that the tiniest mistake in time can create a larger one in the future--these are just a few of the direct actions that help to create suspense.
Bradbury's description of the prehistoric time heightens the foreboding feel that runs throughout the tale. The idea of cheating past actions by avoiding mistakes altogether the second time around is an inherently questionable philosophy with little margin for error. Eckels, the hunter whose courage fails at a critical time, is not a man to count on when the whole future of civilization rides on his weak shoulders. When he turns and runs, the reader knows something has gone wrong. The reader can only wait and wonder what will go wrong next.