A great place to look for support for this question is the section of the story where Christmas is running, basically non-stop for several days after committing his crime. The images that are used to describe his condition focus a great deal more on simple action and reaction and moving on instinct rather than in a more human-like manner.
One of the aspects that I've focused on in the past is the way that he "feeds" rather than eats. The description of the times that he does find sustenance are connected far more distinctly with simply trying to quench his hunger, to answer the call of his stomach than they have anything to do with our more human conception of eating for pleasure or with company, etc. He is simply trying to provide fuel for the fire, eating in a way that is animalistic rather than humanistic. There are plenty of other examples as well.