The opening scene where George and Lennie arrive at a pond. Lennie kneels down to drink the water with his hands.
Carlson convincing Candy to let him kill Candy's dog because of its smell and because of its worthlessness. In reality, Carlson's reason to euthanize Candy's old dog is that he wants to show his power. Another reason is that he wants Candy to be as miserable as he is. Candy is unwilling to give up his dog because that's his only friend.
Curley comes in the room angrily questioning Slim has been with his wife. Lennie doesn't know what is going on and laughs at the wrong time which triggered Curley to beat him. Lennie doesn't fight back until George angrily demands him to. Lennie then loses control busting Curley's hand.
Curley's wife interrupting the conversation in Crooks's room using the excuse of looking for Curley. She backfires at Crooks when he and Candy shame her for not being an ideal woman. Crooks realizes that she is right and he as a black men does not have any rights to speak to her.
Lennie realizes that he has murdered Curley's wife. He is afraid of the people getting mad at him so he decides to run away with the dead puppy that he killed right before Curley's wife.
George finds Lennie after he escaped after the murder of Curley's wife. They talk about their dream then George kills Lennie for Lennie's own good.