full red blood cell is almost entirely hemoglobin. It is essentially a shipping container. A notable paradox of red blood cells is that although they carry oxygen to all the other cells of the body, they don’t use oxygen themselves. They use glucose for their own energy needs. Hemoglobin has one strange and dangerous quirk: it vastly prefers carbon monoxide to oxygen. If carbon monoxide is present, hemoglobin will pack it in, like passengers on a rush-hour
