I think that their physical state is one particular difference between them. Curley is small and jumpy, almost looking for some type of confrontation to mask his own insecurities. Slim is much more deliberate, the kind of man that commands respect when he enters the room, while Curley demands it through his actions and his sense of physical being. Slim is not one to initiate fights and use the arbitrary conflict to represent his own sense of strength. Rather, this is something that describes Curley. Slim is much more thoughtful and one who examines situations, while Curley flies off the handle and succumbs to irrationality at every point. Slim holds the respect of the other ranch hands, and Curley uses his position as the boss' son to try to gain some of this respect. At the same time, Curley is someone who lives in the hope of what can be done and always seems to latch on to some ideal that can help to bring meaning to existence. The obsession with his wife, the desire to beat Lennie, and then the hunt for him once his wife is dead are all examples of this. In contrast to this, Slim is someone who lives in the present, a representation of doing as opposed to dreaming.