A Sound of Thunder by Ray Bradbury takes Eckles 60 million years in the past to the time of the dinosaurs for the purposes of hunting and killing a Tyrannosaurus Rex . Eckles is warned of the dangers and the fact that guides and hunters have died in their pursuits but he is still certain that he wants to go. He knows that the safari company has gone to great lengths to ensure that the eco-system is not altered, even wearing oxygen masks to ensure that no bacteria enters the pre-historic atmosphere, because "destroying an important link in a growing species" could change the future.
Eckles panics at the sight of the T-Rex and strays off the designated path, stepping into some mud. At this stage, however, he is blissfully unaware that, not only his choices, but his subsequent actions, will have had life-changing effects on life as he knows it when he returns to the present day- the year 2055. He believes that offering to pay the safari company should be sufficient. Even when Eckles, on the way "back" to the present day, notices the dead butterfly, he still refuses to believe that it could have any real effect.
The story reminds readers how a self-absorbed attitude and lack of respect can have disastrous results. Thinking that money is a solution to all problems is also a very modern problem. The changes to prehistoric times and the ecological effects on the future describe the well-documented "Butterfly Effect," which results from seemingly small and insignificant changes, often unnoticed initially but which can cause dramatic variations in other naturally-occurring events. This phenomenon stems from Chaos Theory and the unpredictable progression of a hurricane.
The link with the title and its appropriateness is revealed because thunder can be understood in terms of what it represents. Thunder warns us that bad weather conditions exist and are possibly approaching. Sometimes the bad weather moves away and other times it gets ever closer until it reaches our location. The thunder is not the problem, but the weather it brings with it, is. So too in A Sound of Thunder. The potential for disaster was there but was not imminent. Only Eckles' selfish actions set the changes in motion.