Why A Cat? Or A Badger? Or a ...?

I was reading Yoko's Show and Tell to my daughter who was home sick from camp when we started talking about the fact that Yoko and her family are cats.  My daughter pointed out that "they are so much like people that when you get really into the book, you forget they are cats."  Which begs the question, why make them animals in the first place?  And if an animal, why cats?

The same question could apply to many other books but the Frances books  by Russell Hoban immediately spring to mind.

Well, to find out, we went to the source.  My daughter wrote a letter to Rosemary Wells, asking her that very question.  I'll let you know if we hear back!

In the meantime, I'm asking all of YOU that question. Why do you think Rosemary Wells chose to make Yoko a cat?  Why did Russell Hoban choose to make Frances a badger?  Would the books work as well if Yoko were a bird?  If Frances were a kangaroo?

What other books come to mind with animal protagonists so successfully anthropomorphized that you (nearly) forget they are not human?