This is what you are not to eat… (Leviticus 11:4)
In the previous mitzvah, God commanded that we are only to eat animals displaying the two signs of being kosher: chewing the cud and completely split hooves. We said that this is a “lav haba m’klal asei,” a prohibition inferred from an obligation. The Rambam tells us in Sefer HaMitzvos (Negative #149) that a prohibition inferred from an obligation is a positive mitzvah (i.e., “Thou shalt”). Here we have the negative mitzvah (the “Thou shalt not.”)
This verse, through verse 7, prohibits eating four animals that are known to have one sign of kashrus or the other. There are three that chew their cud but do not have split hooves. They are commonly translated as the camel, the hare and the hyrax or “rock badger.” (Hares do not chew their cud the same way that cows and camels do. Rather than bringing up food from one of several stomachs, rabbits and hares excrete what are called caecal pellets and chew them in a process called reingestion. The bottom line is the same: they eat food that that they’ve eaten before.) The pig has split hooves but is not a cud-chewer. (This is why the pig is the prototype of non-kosher animals. It’s not inherently any less kosher than camels, horses or dogs. However, a pig presents the external trappings of a kosher animal. As the Midrash Rabbah says, the pig is metaphorically more reprehensible because it sticks out its foot and says, “Look! I’m kosher!”)
While the verses here only mention four animals, it is not intended as an exhaustive list of those we may not eat. The intention is that we may not even eat these animals that have one kosher sign; we certainly can’t eat those that don’t have any!
As we said in the previous mitzvah (and several times before), the reason for this mitzvah is that God is warning us away from things that would be spiritually harmful in the same way that our doctors would warn us about eating things that are physically harmful.
This mitzvah applies to both men and women in all times and places. It is discussed in the Talmud in the tractate of Chulin (59a-b). It is codified in the Shulchan Aruch in Yoreh Deah 81. It is #172 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #93 of the 194 negative mitzvos that can be fulfilled today as listed in the Chofetz Chaim’s Sefer HaMitzvos HaKatzar.