[RIjdrVs3]

I ask these questions out of ignorance, so please don't take offense.
I have heard that Muslims consider dogs to be "unclean" and never have them as pets.

So I am wondering:

* Is this truly a belief in Islam, or is this is just a cultural norm from countries that happen to be predominantly Islamic. In other words, is there something in Islamic theology about dogs or is it just a cultural tradition from different countries.
* Does this belief or tradition vary from place to place? I know Islam exists all over the world.
* Do some Muslims have dogs for pets?
* What does "unclean" mean?
* What do Muslims think about dogs and how they should be treated?


I have read a couple things:

* Muhammad had a cat.
* Muhammad once protected a female dog who was giving birth so that no one would disturb her and her puppies.


I don't know if those are true.