Leech knows that outside the Ferrarium, people eat the flesh of animals. The thought makes her sick; or rather, she expects it to make her sick, and feels guilty when it doesn’t.
The blood girls eat only their garden vegetables, and flatbread, and drink milk from their goats. The life they grow within themselves is only once removed from the pure earth. So long as they remain pure, the blood they give the Honchos is once-removed as well.
This is sacred doctrine, and Leech never questions it. She only wonders, watching the returning Honchos, how all that purity is spent.