When the time machine lands, the travelers notice the change in their environment and realize they have indeed traveled far back in time. Travis points toward a metal path that goes into the deep forest. He explains to the riders that they must stay on this path, never leaving it. It floats six inches above the earth, and any deviation from the path can have disastrous results.

They are not to touch one blade of grass, flower, or any other living organism. The hunters are told that they cannot kill any organism that is not approved by the company because it might trigger a chain of events that will affect the future. The only animals the company approves for hunting are those that would have died within two minutes in the natural course of events. Any failure to follow these rules will result in a penalty, and the company will have to report the incident to the government.

Accidentally killing a mouse, Travis tells them, would mean that the mouse’s family line would end. That, in turn, over the course of time might lead to fewer mice, causing starvation among the foxes who feed on them. This, in turn, might eliminate other creatures further up in the food chain. Ultimately, the death of that one mouse might impact humans and lead to the elimination of a complete civilization. Even killing a few plants or introducing a microorganism from the future could lead to unimaginable changes in that future. Travis explains that this is why they wear helmets, although he also notes that these predictions are only theoretical. No one knows the actual consequences yet.

After stepping out of the time machine, Eckels becomes excited. He wants to shoot a Tyrannosaurus right away. He carelessly plays with his gun, and Travis scolds him. Everyone is reminded to stay on the path and not to shoot until they get orders. Travis points toward the Tyrannosaurus, which has been marked with red paint for easy identification. On seeing the dinosaur, Eckels panics and starts losing faith in his ability to shoot it. Its size and strength overwhelm him. There is silence, except for a “sound of thunder” as it walks, and it is described as “a great evil god, folding its delicate watchmaker’s claws close to its oily reptilian chest.”

 In a state of panic, Eckels freezes, saying it can’t be killed. He asks Travis to get him out, regretting his choice to come on the safari at all. He steps off the track and returns to the time machine, where he hides.

As a result of the sudden chaos, the Tyrannosaurus notices the men and charges them with a terrible roar. The others manage to point their rifles and shoot it. The creature falls with a loud noise and splatters blood over the men. Billings and Kramer vomit. They hear another loud sound of something falling. Lesperance points out that it is the sound of the giant tree that was supposed to fall on the Tyrannosaurus, killing it. He asks Billings and Kramer if they want a trophy picture with the Tyrannosaurus, but both refuse. They cannot bear to look at the mutilated body of the dinosaur.