Blood
Fresh animal blood, in the Himalaya usually from yak, sheep or goat, which sets when heated and gives sausages and pan dishes body and a deep, iron-rich flavour.
Fresh blood is usually available only to order from a butcher, most often pig's blood, less often lamb or beef. Ready-cooked, set blood in cubes sometimes turns up in Asian shops, and frozen blood in Eastern European grocers.
Substitute:
There is no true substitute, because nothing else both binds and tastes like this. For fried dishes, set blood cubes from an Asian shop work, but they can no longer be stuffed into sausages.