After 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 their effect on events when they go back, since tiny alterations to the distant past could snowball into catastrophic changes in history. The hunters must stay on a path to avoid disrupting the environment and only kill animals which were going to naturally die at the same time.
Despite his earlier eagerness to begin the hunt, Eckels loses his nerve at the sight of the T Rex. Travis tells him he cannot leave, but Eckels panics and veers off the path. The two guides kill the dinosaur, and shortly afterward, the tree that would have killed the dinosaur in the absence of human intervention falls on the corpse. Travis' elation quickly changes to fury when they find Eckels and see his muddy boots, which prove he went off the path. Travis threatens to leave Eckels in the past unless Eckels removes the bullets from the dinosaur’s body, as they cannot be left behind.
Upon returning to the present, Eckels notices subtle changes. English words are now spelled strangely, people act differently, and, worst of all, Deutscher has won the election instead of Keith. Looking through the mud on his boots, Eckels finds a crushed butterfly, whose death was apparently the cause of the changes. He pleads to Travis to take him back into the past to undo the damage, but Travis refuses and fires his rifle. It is left untold what he shoots, although it is presumed that he kills Eckels. The dark ending reveals that the title not only refers to the