Why are the maus characters portrayed as animals?

They are portrayed as animals because Speigelman is trying to convey the idea that putting a stereotype on a group of people, like the Nazis did, is ridiculous. All of the people in the group are not the same. Since the people were portrayed as animals, they could not have any distinctive characteristics to make them stand out from the next person. Basically he is saying that what the Nazis did was ludicrous and that each of the people who were victims of the Holocaust had their own story. Also, since the Nazis were depicted as cats and the Jewish people were depicted as mice, this shows that they are naturally enemies seeing as though cats and mice are natural enemies.