There’s a god, one of the older, minor ones. I don’t remember his name, no one does. If they did he’d still be around, because that’s how it works. Anyway, he used to demand a blood sacrifice from his adherents. It had to be daily, and it had to be their blood. It couldn’t be the blood of a doe or a lamb or a captured warrior or anything else; it had to be from them.
So, you do the math. They all died of anemia. The smart gods, they don’t make it fatal to worship them. That’s just stupid.