Substitute for blood? We're working with some 16th century recipes for sauces that call for blood (among other things). However, several members of the group try to keep kosher, and besides, I have no idea where or how one would acquire blood for cooking.

I know I can substitute egg for the protein/thickener aspect, but what about the flavor? What does blood actually taste like (when cooked)? I've had blood sausage, but all I remember about its flavor is the generous quantity of black pepper. Would a red wine and some salt come anywhere close?
Depending on the animal, blood would impart a somewhat metallic taste and a certain “richness” - not really the umami-meatiness of red meat, more like the earthiness of liver - with a slight sweetness. 

The flavor profile will be quite different depending on the animal, with pork being more neutral than the more intense and metallic beef.

A substitute would depend on the recipe. But the acidity of red wine is very much not what blood would contribute to a dish. If the binding properties are to be ignored, think “beets plus sautéed mushrooms”, as a very, very vague flavor approximation. But if your sauce is rich per se, you can probably just skip the blood without doing much culinary harm.