Is this the dinosaur we have been sent here to hunt?
In the beginning of the story Eckels meets the tour guide, Travis, Travis starts telling Eckels the rules of the Time Safari, and what Eckels should ans should not do during their time in the different era.
In this part of the story the reader learns that the people that have come hunting cannot go off the path because if they were to get off the path then there future era would get affected and the everything would change.
In this section the men have arrived to the old era where dinosaurs would roam the earth, and they are trying to find the dinosaur that they have been sent to hunt. Eckels thinks that the job will be simple because he has gotten plenty of practice hunting other animals, when he meets the dinosaur Eckels starts to panic.
The men have shot the dinosaur but Eckels has run off the path, now everything will change because in the process of getting off the path he killed a butterfly and that butterfly affected his future era.
Travis was very upset because Eckels run off the path, he asked everyone to take a vote, if Eckels would stay and go to their era or leave Eckels behind because he broke the rules and now he would pay for what he did, in the end they take Eckels back, but Travis is still mad at him for stepping off the path.
In the end all the men returned alive to their current era, but everything was different because of Eckels killed the butterfly. Travis was enraged at Eckels and decided to shoot and kill him, that was the "sound of thunder".