How are the animals chosen in a sound of thunder?

Eckels does not understand why they have to be so careful, so Travis gives a lengthy explanation about how one animal being killed could quite possibly cause the death of billions of future organisms.  Eckels then asks how the safari company decides which animal they are going to hunt in the first place if any animal death is such a big deal.  Lesperance explains that he goes back and tracks an animal that is about to die from natural causes. By doing this, he knows that no animal is depending on it for food, and he knows that it will not mate again. Because the animal is going to die within minutes anyway, its death from hunting will not affect the time stream.

Explanation:

well for some you have to do on your own on a paper but yeah

we need to see the paragraphs in order to answer this.