<P> In the year 2055, time travel has become a practical reality, and the company Time Safari Inc. offers wealthy adventurers the chance to travel back in time to hunt extinct species such as dinosaurs . A hunter named Eckels pays $10,000 to join a hunting party that will travel back 66 million years to the Late Cretaceous period, on a guided safari to kill a Tyrannosaurus rex . As the party waits to depart, they discuss the recent presidential elections in which an apparently fascist candidate, Deutscher, has been defeated by the more moderate Keith, to the relief of many concerned . When the party arrives in the past, Travis (the hunting guide) and Lesperance (Travis's assistant) warn Eckels and the two other hunters, Billings and Kramer, about the necessity of minimizing the events they change before they go back, since tiny alterations to the distant past could snowball into catastrophic changes in history . Travis explains that the hunters are obliged to stay on a levitating path to avoid disrupting the environment, that any deviation will be punished with hefty fines, and that prior to the hunt, Time Safari scouts had been sent back to select and tag their prey, which would have died within minutes anyway, and whose death has been calculated to have minimal effect on the future . </P> <P> Although Eckels is initially excited about the hunt, when the monstrous Tyrannosaurus approaches, he loses his nerve . Travis tells him he cannot leave, but Eckels panics, steps off the path and stumbles into the forest . Eckels hears shots, and on his return, he sees that the two guides have killed the dinosaur, and shortly afterward the falling tree that would have killed the T. rex has landed on top of it . Realizing that Eckels has fallen off the path, Travis threatens to leave him in the past unless he removes the bullets from the dinosaur's body, as they cannot be left behind . Eckels obeys, but Travis remains furious, threatening on the return trip to shoot him . </P> <P> Upon returning to 2055, Eckels notices subtle changes--English words are now spelled and spoken strangely, people behave differently, and Eckels discovers that Deutscher has won the election instead of Keith . Looking at the mud on his boots, Eckels finds a crushed butterfly, whose death has apparently set in motion a series of subtle changes that have affected the nature of the alternative present to which the safari has returned . He frantically pleads with Travis to take him back into the past to undo the damage, but Travis had previously explained that the time machine cannot return to any point in time that it has already visited (so as to prevent any paradoxes). Travis raises his gun, and there is "a sound of thunder". </P> <P> The story was aired on The Ray Bradbury Theater on October 8, 1989 . </P>

A sound of thunder what is the sound of thunder at the end of the story