In the sixth aliyah G-d gives the commandments of what constitute kosher and unkosher animals, fish, and birds. Rashi says that with these commandments, G-d is separating the Jewish people from uncleanness. The Torah says that animals have to have both wholly cloven feet, and chew their cud. The Torah lists four animals that have only one of these attributes, but not both, and are therefore completely unkosher. The Talmud states that these are the only cases we will ever find of animals having only one of the two attributes of kosher animals.

It is interesting to note that only one animal of these four has wholly cloven feet, while the other three chew their cud. The one with the wholly cloven feet is the pig, which is considered the prime example of an unkosher animal. This is ironic, since it has half the signs -- and the external one, at that -- of kosher animals, so why should it have the notion of being most unkosher, more than other nonkosher animals? The reason is that it poses the greatest threat. This is so because it looks kosher, and someone can make a mistake and think it's kosher when it is not at all. In fact the pig sometimes sits on its bottom, with its feet sticking out, as if to show off and emphasize it's kosher sign and tempt people.

This is the same danger of missionary organizations that "appear" Jewish, having "Oneg Shabbat" or a Pesach seder, even men wearing tzitzis, all Jewish outward signs, while the ulterior motive is to coax the Jew into straying toward another religion.

This aliyah goes on to say that fish have to have fins and scales. It follows that shellfish, among others, are not kosher.