In Ray Bradbury's story "A Sound of Thunder," the character Eckels is a time traveler who goes back in time to hunt dinosaurs. However, he is warned to "stay on the path" and not to deviate from it, as any small changes in the past could have disastrous consequences in the future. Despite this warning, Eckels panics and steps off the path, killing a butterfly in the process. When the time travelers return to their own time, they find that the world has been drastically altered, with language and political systems changed as a result of Eckels' actions.
The theme of the story is the concept of the butterfly effect, the idea that small events can have far-reaching and unforeseen consequences. This is exemplified by the way in which Eckels' seemingly insignificant act of stepping off the path and killing a butterfly leads to major changes in the future. The story is a warning against acting recklessly and without considering the potential long-term effects of our actions. It also serves as a reminder of the interconnectedness of events and the importance of being mindful of the choices we make.