The Rat

The rat is on Joe's face because he was imagining it. Even though we never truly know if he does feel a rat or not, I believe that he just imagines it. Joe has a fear of the rat. Joe first encounters the rat when he sees it eating the dead soldiers face. That permanently connects the rat with death for Joe. The rat also signifies Joe's helplessness to do anything about it. The main concern at the time for Joe is that the rat will begin to eat his face and he cannot prevent it, but there are many different interpretations you can pull from this scene. The problem Joe encounters with the rat is that he cannot tell if it is reality or a dream, which makes him realize his dilemma of not being able to tell time. Once Joe can understand if he is awake or asleep, he'll know what is real and what's a dream. For Joe, the rat means many things, but most of all it represents a helpless death which he fears the most.