Enbrethiliel has a good post up about animals and God. (It must be good; she links to me.) :)
It is lucky for dogs that we Catholics accept Jewish scriptures written in Greek — because Jews in Israel didn’t think much of dogs, but the writer of the Book of Tobit thought that of course Tobit should have a dog. So if you’re Catholic or Orthodox, pets are scriptural. If you’re not, you have to rely on human tradition. ;)
Here’s an interesting article on the Book of Tobit in the Dead Sea Scrolls and St. Jerome’s tail-wagging addition.
Cats have been important helpers of humanity for a long time, and Pope Benedict XVI isn’t the only churchman who’s liked them. For example, there’s the 9th century Irish monk at Reichenau who wrote a little poem about his cat, White Pangur (Pangur Ban). (More translations.) Apparently Pangur Ban (along with his monks) is a main character in an old kids’ Celtic fantasy series by Fay Sampson. Looks interesting.