You can't kill anything that i don't tell you to. If i say don't shoot don't shoot.
Climax
Resolution
The characters Travis and Eckels talk about what needs to be done, and what can't be done
"No, it can't be. Not a little thing like that. No!" Embedded in the mud, glistening green and gold and black, was a butterfly, very beautiful and very dead
Travis shoots eckels, because they find out that Eckels killed a butterfly when he fell off of the trail.