I was always told that the reason that certain cultures don't eat pig is because they are dirty animals, which makes sense, although that could be a "cover up"? lol
And I think the same goes for dogs in Islam; they cannot be kept in the home, but can be used as guard dogs, and this is because they are dirty. Or something like that. I could be wrong.
-Ben
As a Muslim, here are my thoughts
Pigs: haraam (forbidden) animals. They're very dirty because they wallow in mud and feces and their flesh is infested with parasites.
Also, in Islam, animals have to be killed a certain way. The animal is hung upside down, the person killing the animal says "bismillah" ("In the name of God") and then slits the animal's throat. This death is instant because the blood immediately drains from the head, so there is no suffering for the animal. And since there is no suffering, the meat isn't tough because the animals tense up when they are being slaughtered any other way.
Pigs don't have a throat to slit, so that's another reason why we don't eat them.
As for dogs, their saliva is impure (because they lick their crotch to clean themselves), so if a dog licks us, we have to wash that spot 7 times to make sure all the impurities are washed away.
That being said, I'm personally a dog lover. Look at how cute these pooches are:
All I know is in Islam is dogs are unclean according to the Koran.
Not according to the Qu'ran (I think), but there is a Hadith (saying) of the Prophet Muhammad (SAW) that dog's saliva is unclean.