I’ll let the great moderate Ayatollah Sistani say it:
The following ten things are essentially najis [unclean]:
4. Dead body
8. Kafir [unbeliever — i.e., non-Muslims]
9. Alcoholic liquors
10. The sweat of an animal who persistently eats najasat [unclean things].
From FoxNews (thanks to all who sent this in):
A 70-year-old Iranian man was arrested and sentenced to four months in jail and 30 lashes for walking his dog, Adnkronos.com reported Tuesday. Police caught the man on the street with his dog in Shahr Rey, a suburb of Tehran.
Owners of domestic animals are forbidden from taking them on the streets of the city because Islam considers dogs to be impure. An Islamic judge later charged the man for “disturbing the public order,” Adnkronos.com reported.
Despite repeated warnings by the police, dog owners continue to defy authorities by taking their dogs outside their homes. Typical punishment for people caught with dogs outside is a fine or the “detention” of their animals in a pound, Adnkronos.com reported.