In this situation George is very upset at Lennie for keeping a mouse and killing it as well. George has no patience for Lennie and his games killing these mice and wanting to keep them. This shows how George must take care of Lennie as a child and care for his special needs. This shows great understanding and maturity.
Chapter Six: Pg 102
Tell me like you done before.
Lennie went to the barn to see the puppies and goes into Crooks's room. Crooks is asking Lennie about his life with George and how there relationship is different compared to the rest of the men on the ranch. This theme is talking about trust and friendship. Lennie and George are unlike everyone else because of their strong bond.
Curley's wife is upset and needs to talk to someone instead of being isolated. She talks to Lennie about how badly her husband treats her and also her past and why she married Curley. This shows the importance of human interaction. Curley's wife needed someone to talk to and Lennie was kind and listened until he killed her by accident.
The scene happens right after Lennie has run away after killing Curley's wife and George finds and kills him. George tells Lennie to look out and visualize the dream while behind him. George shoots Lennie killing him. George wanted to save Lennie from Curley. This is true friendship.