During this scene George and Lennie are sitting by the campfire in the clearing. Lennie then finds the mouse that George threw over the stream earlier and decides to keep it and pet it. However George finds out and takes it away because Lennie tends to kill small creatures. The theme is that you can do something bad without realizing it.
In this scene Slim is starting to converse with George and Lennie. Slim is also quietly impressed by their friendship, appreciating the fact that they look out for one another. The theme is that good friendship can show a lot around people.
In this scene Carlson shoots Candy's dog because Candy's dog was really sick and old and Carlson wanted to put the dog out of it's misery. The theme of this is to put things out of their misery no matter how much it hurts you so they can be free.
In this scene Lennie walks into Crooks' harness room. Crooks didn't want him there in the first place but he let him in since Lennie wanted to give him company. Crooks talked to Lennie about his childhood and it started to make Lennie dream about owning the farm. The theme of this is that people always need company but they never say they do.