Kashrut, in a nutshell
My rabbi explained the dietary laws this way:
1. No predators;
2. No bottom-feeders;
3. No blood;
4. Humane butchery of all animals not otherwise prohibited.
Rule #1 is topical to this thread.
Rule #2 incorporates swine and shellfish.
Rule #4 includes, but is not limited to, the famous (and oft-repeated) commandment: "Thou shalt not seethe a calf in its mother's milk".
Rule #3 does not explain why Worf's adoptive parents, the Roszhenkos (obviously Jews of Russian origin - you may recall, Theo Bikel portrayed Worf's father) made such good blood pie.