I am not sure exactly what happened on these pages, but another touching incident is the actual killing itself. Steinbeck begins by showing us Lennie alone in the barn with a dead puppy. We immediately feel for him, but then Curley’s wife comes in and we feel sorry for her. When he kills her accidentally, it is because she is lonely and misunderstood, just like him. A very sad moment.
Are these the last five pages in the edition you are reading? Assuming they are, the situation at the end of the book presents us with a man (George) forced into a difficult decision.
Lennie has committed a murder, again, and his punishment is almost certainly going to be death when he is found. George's decision is to either (1) kill Lennie himself to avoid the ugly and frightening confrontation that will ensue if Curley finds Lennie or (2) let that confrontation happen. There is no good option. This is somewhat tragic.
In this last episode of the book, Steinbeck presents us with two types of innocence and this is, for me, a big part of what makes the book tragic. Lennie is incapable of curbing his behavior. He did not kill out of malice, but out of a childlike fear and rage. He is innocent of any deep evil, though he is a murderer.
George has done nothing wrong, except to help Lennie escape punishment in Weed. George is responsible for Curley's wife's murder in a way, though he has no blood on his hands.
The nature of each man's innocence is fully articulated in the scene as George tells Lennie to think about rabbits then shoots him, with mercy.