I never actually thought blood sausage was made of blood. I just assumed it was from redness of meat or coloring. The blood is used to congeal the sausage like egg whites would. I loved blood sausage as a child and had not had it in decades. I wonder what holds together other types of sausages since blood holds blood sausages together. I believe this and its relatives are the only food we eat blood. Since it congeals a sausage like egg whites I wonder if beef blood would be a good substitute for egg whites, health wise.