Blood can also be used as a substitute in baking. Pretty sure it's in lieu of eggs. Not curious enough to ruin a perfectly good batch of brownies though :(
That was a "fine enough" substitute before commercial egg replacers got as good and commonplace as they are now. I'll still do it for some recipes as I like the added apple flavor and moisture, but I generally use Ener-G Egg Replacer for replacing eggs in a dough mix and maple syrup for egg washes when vegan baking these days.