We hate to break it to you, but the animals you have come to know and love are fictional. Mice can't talk, rats can't really be engineers, and owls never befriend small, furry mammals. Sad as it might be, we humans are stuck in a world where we have a monopoly on things like speech, electricity, and the Kardashians.
Perhaps one of the reasons why Rats is such an appealing story is because it imagines a world in which humans don't have a monopoly on all of those things. The animals we meet all have very human characteristics: they love their families, they get scared, they're brave, they're loyal, they like to read, they're curious. You get the picture. They are basically tiny, fur-covered humans who live underground, scurrying around thinking brilliant things.
A good question to ask about this might be "Why didn't the author just write a story about humans if he likes humans so much?" First of all, you could never fit a human family in Mrs. Frisby's cement block, so there's that. But a more important reason is that using personification makes us ask, "What if animals do have those feelings and we'll never know?" Since this is a book that cares a lot about animal rights, it makes sense that it would want readers to think along those lines. (See how we just personified the book? Shmoop is sharp like that.)
We all know stereotyping is bad, but in this book, animals fall into pretty recognizable roles: The Owl is wise and distant when he tells Mrs. Frisby to "go to the rats" (8.27). The cat is a soon-to-be-felon, even while he dozes in the sun. The rats (though we love them) are always stealing from humans and getting into their stuff. The shrew is… shrewish.
So why the stereotypes? Why are we judging books and owls and shrews by their covers? Think about it this way: a world inhabited by talking rats and mice is a little strange. Anchoring these animals to familiar stereotypes helps keep this little animal kingdom from feeling totally chaotic and new. It also makes a good point about stereotypes in the first place: they aren't always accurate, right? The shrew may be shrewish, but she's just protecting her friend. The rats may steal, but they have a Plan, too. How's that for busting up the status quo?