I think that the incident where Candy's dog was about to get shot forshadows the death of Lennie Small. It seemed as though the dog’s life were controlled by others and it had no say in anything, so in this episode I believe the dogs fate was controlled by Slim. This is because Carlson was looking up to him for approval for the dog to die, but on the other hand Candy was also looking up to him to see if he could help him out as it says "Candy looked helplessly at him, for Slim's opinions were law." So Slim agrees with all the others that it is best for the old dog to go and be even said if he was a cripple like that he would wish that someone would put him out of his misery. This is where Candy gives in as he realises that there is no reversal for this incident now. Whit enters and tries to help out before this aswell by changing the subject to an article written in a magazine. Yet Carlson refuses to be distracted so he sped up the process by not taking no for an answer. When Carlson takes the dog outside George and the others try to cheer up Candy but Candy just blanked out everything and rolled over silently.
This paragraph is just like the end but the in the end George takes on board what Candy had to say" I should have killed my dog instead of some stranger." In the end everyone was looking to kill Lennie but George loved him just like Candy had loved his dog so he wanted to kill Lennie instead of some strangers. He knew Lennie was always going to end up in this situation again so it had to be done, just like how everyone could no longer bear the dog to be around smelling up the place. Just like the dogs fate was controlled by Slim, Lennie's life was controlled by Curley who wants him to be destroyed.
The main idea that is in this passage is that 'The weak will be disposed by the strong.' This doesn't mean in physicality but in the sense that Curley has more power anyway and now that Lennie killed his wife Curley believes he has a