Sheep are cloven-hoofed animals, meaning that each hoof is made up of two parts separated right down the middle. Other animals that have cloven hooves include: Deer, gazelles and antelope; Alpacas and llamas; Cattle and buffalo; Goats; Pigs. Note that all of the animals listed except pigs are grazing/browsing ruminants that "chew the cud" so would be considered "clean" according to the book of Leviticus. Pigs are cloven hoofed, but they are also omnivorous and have a digestive system quite similar to our own. Therefore, they are not considered "clean" by this standard.