What is the significance of mice and cats in the book Maus?

The graphic text uses the extended allegory of anthropomorphized mice—Maus in German—to represent Jews, cats to represent Germans, and other suitable animals to represent other nationalities or ethnicities.

In Chapter One and throughout the remainder of the graphic text, Vladek and other
Jews are illustrated as mice, giving the text its German-language title of Maus. Mice are a suitable and obvious choice to represent a people who were heavily persecuted during the Nazi Holocaust. Poles are illustrated as pigs, indicating their essentially selfish nature from the viewpoint of the Jews—throughout the graphic text, many Poles will sacrifice Jews for often trivial personal gain.

In Chapter Two, the illustrations of their train ride include Nazi flags, swastikas, and jack-booted Nazi troopers who are illustrated as cats, an apt symbol for the Nazis who will prey upon the Jewish peoples illustrated as mice.