Theressa B. answered 03/21/20
Bachelors in Comparative Literature
I think the answer is entirely subjective.
There can be immediate deductions drawn, as you pointed out in the case of the German's as cats (predators) and Jews as mice (prey). In addition, the French have historically been referred to as frogs, and Spiegelman is also potentially referencing to other literary works, namely, in the Poles' portrayal as pigs, which may link back to Orwell's depiction of soviets pigs in Animal Farm.
But there are other answers too, and thinking critically about the symbolism behind these artistic decisions will help better your understanding of the book itself. For example, think about what it means to create caricatures out of groups of people who were implicated in the Holocaust. By organizing each group of people into a species from the animal kingdom, Spiegelman might be commenting on what such categorizations or hierarchies mean in a society. By pointing these distinctions out so explicitly, readers are forced to question them, just as you have.