Via Atlas Obscura: “Is This Duck Kosher? It’s Complicated“:
THE BASICS OF JEWISH DIETARY law—the laws of kashrut—are fairly well-known: no pork, no shellfish, no milk and meat together. But there are many, many more laws than that, some of which are unclear, some of which are localized and don’t necessarily apply to all countries, and many of which have never really been settled. The case of the Muscovy duck is one of the most fun.
The rules of kashrut have a couple of issues that destabilize the entire process of figuring out what Jews can and cannot eat. One of these fundamental issues is that the laws don’t necessarily follow any larger philosophy. Jewish scholars have long divided the laws of Judaism into a couple of different categories. Mishpatim—the –im and -ot endings of words signify plurals in Hebrew—are laws that are self-evident to the survival of a society, like “don’t murder” or “don’t steal.” The edot are laws usually surrounding holidays, symbolic rules designed to memorialize events or bring a community together, like wearing a yarmulke or not eating bread on Passover. And then there are the chukim.
The chukim are laws that make no sense. They are sometimes phrased in ways to make following them more palatable; for example, that these are laws passed down directly from God, and it is not necessary that we understand them. The rules of kashrut are sometimes, but not always, placed in this category.