I enjoyed this film for a number of reasons. Its use of black and white lent an ominous, dark tone to the piece, very appropriate for a post-apocalyptic time. I also liked the irony of how, at first, the mother and daughter consider the man a dog and the husband charges that he's a man, and then, at the end, mother and daughter desperately proclaim he is a man while the husband insists he's a dog.
Could the man-dog represent the irrationality and absurdity that humanity has sunk to as a result of a nuclear war? This idea is reinforced by the fact that his existence as we see him is never explained--then again, that could be part of the idea--no explanations, therefore irrationality. Even if he does represent this notion, I think that there is still a ray of hope that the movie is trying to show--though absurd, the man-dog is not threatening, and is pleasant to be around. Ironically, the "human" husband is the one who is unpleasant and barbaric.
Finally, the fact that we still pity the man-dog at the end says very much. The film ultimately ends with the implied death of the man-dog, whom the father and sons murder, symbolizing, perhaps, that humanity will never change, and that mindless hatred and competition will always dominate kindness, thought, and beauty.
