Aariz A: Dog

Carlson probably suggested to shoot the dog to put it out of its misery, and to save it from future incidents. I think this was because all the dog does is sit in a doorway. He has nothing to do on the ranch. This could symbolize this happening to Lennie, George, Curley's wife, or even Curley, This is so because one of these people might do something that could cost them their life. For example, Curley could hurt Lennie, and George might have to defend Lennie by attacking Curley.