This is surely one of the best accounts of the Holocaust I have ever read, and the incongruous way in which it is narrated in comic strip form and through the use of animals really helps to develop the characters that the story focuses on. The basic idea is that Spiegelman wants a different way to present the Holocaust and the way that Jews were relentlessly pursued, captured and exterminated by the Germans. Animals imagery is what he turned to in order to emphasise this fact. Therefore animals are used to represent the major races. The cats are the Nazis and the Jews are depicted as Mice. This greatly helps to emphasise the way that the Jews were seen as vermin who needed to be hunted down and killed.
Depicting the Jews as mice emphasise their vulnerability and also the way that they were regarded by the Nazis. Depicting them as cats clearly indicates the link between the two races and how the Aryan race saw themselves as superior and also responsible for eradicating mice (the Jews) from the face of the earth. This technique also helps highlight the immense sense of helplessness that various Jewish characters feel. They are vulnerable and exposed in this terrible world, and they know it.