Boniek Bajerocki
Boniek Bajerocki voted up Don Barzini's answer

Pigs live in filth, eat anything including filth, and are therefore considered unclean. Any amount of time spent around live pigs leaves no doubt about this logic. 

I had a Muslim friend tell me once that pigs are physically incapable of looking up toward heaven, so are considered too lowly, beneath Allah's grace.

Boniek Bajerocki
Boniek Bajerocki voted up Rooster Cogburn's answer

In the Muslim's divine book, The Holy Qur'an forbids the consumption of pork meat, but even more astounding is the fact that Christians are forbidden to eat it too: “Leviticus and the swine, as he divideth the hoof, and be clove footed, yet he cheweth not the cud; he is unclean to you.

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