If your dog put on trousers and brought you the morning paper and a cup of coffee, you probably wouldn't accept them quietly and start reading the sports page. While most characters in literature who encounter talking animals aren't that nonchalant about it, they seem a lot more accepting of bizarre phenomena than most real people would be. Is it just because they're characters in books? or is it because animals actually have quite a bit to tell us about human nature and the realities of the world we occupy?
There are real-life precedents for talking animals—parrots can speak, crows can acquire human vocabularies, and Balaam's donkey carried on a conversation with the reluctant prophet. Granted, birds with the vocal capacity for imitative speech and supernaturally gifted pack animals aren't really in the same league, but you get the idea. Just because most animals don't talk doesn't mean none of them can.
We're not suggesting Narnia is a real place, or rabbits actually have detailed mythologies, at least not in the sense most people would use words like "real" and "actual." But there are books about Aslan, and there are books about Bigwig and Fiver, Matthias the Mouse, and Mr. Toad, and in that sense those places and characters are real and actual. More importantly, what they tell us about life itself (through their stories, not over afternoon tea) is often true and real and actual.
Basically, stories about animals who apparel themselves in anything other than their own skin and fur, animals that fight with swords instead of claws and teeth, animals who bake their food rather than eating it raw or off the ground, animals that speak (either to humans or each other)—any story we carry of this kind will be found here. While animal fantasy shouldn't displace all other reading, it's important to remember that, in the end, there's very little meaningful difference between a character like Tom Sawyer and one like Abel the Mouse.