You Are What You Eat
Do not eat anything you find already dead. You may give it to an alien living in any of your towns, and he may eat it, or you may sell it to a foreigner. But you are a people holy to the Lord your God. Do not cook a young goat in its mother's milk.
Food that is kosher or halal is prepared according to very strict ritual practices. One of those rituals involves the separation of milk and meat. There are rules regarding how to slaughter an animal, which animals you can eat, and how to have a diet where dairy products are not eaten until after meat has been digested.