For religious/magic purposes, I need a way to draw blood from a human without any tools other than rocks, fingernails, or teeth (i.e. biting with human mouths, not animal/monster teeth). There is no metal available.
I would prefer not to have flint available, but I will if necessary.
Is there a way to draw blood that is plausible? It would be okay for the blood draw to be messy, but it can't maim the person.
The answer bores down to how much blood you would need, but bone is an excellent choice. It can be made sharp, is able to handle time and by the time it's worn beyond use there is enough bone in many hunter gatherer tribes to try to make something new.
If you need only tidbits, you can suffice with a needle. It is common practice to stab a patients finger and catch the blood welling up. If this is not enough blood initially, you can get quite some millilitres extra by massaging the finger certain ways.
Keep in mind that with such technology even an innocent prick can lead to infection and death. You can of course have a ritual or primitive knowledge to have them disinfect the tools via fire beforehand, and some herbs and specific molds laying around, but in general you just don't want to be stabbed for blood. It isn't a huge chance every stab to get infected, but with many attempts and normal life adding other scratches and dirt the chances of dying before you're 20 have skyrocketed. Bone has an ok resilience against heat by the way.
If you want more like the 500ml they take at an current day blood drawing I would say you need a lot of extra people. You can draw blood with hollow needles like we do now, albeit probably bigger, the chances of death are much higher. You deprived someone not just of blood, but of a lot of other stuff as well. Iron deficiency and other complications are just around the corner. Again, in this primitive setting you do not want a single complication. Each has an significant enough chance to be part of the cause of death of someone. And this is after a single blood letting.
For collecting drawn blood you can have rocks worn down in a certain way, or possibly skulls or certain leaves if they're lucky.
That's the tool you're looking for. In modern times, of course, these simple tools are made from metal. Regardless of the material used, what you'd be looking for is a simple, relatively small blade that can be used to open a blood vessel in a relatively non-lethal fashion. Here on Earth, back during the days of Heroic Medicine --- when the patients where the heroes for actually stepping foot inside a doctor's clinic --- bloodletting was all the rage. If the patient was too depressed they'd let some blood! Too excitable? Let some blood! Too fat? Let some blood! Too skinny? Let some blood! You get the idea.
Journal of Lancashire General Hospital
Fleams can be made from anything that is sufficiently sturdy, can hold an edge and can cut through skin and subcutaneous tissue. Obviously metal will work. Stone flake blades will work and are generally small enough to be effective. Wood, bone, antler and horn can also be made sufficiently sharp and pointy.
If your world has creatures with any kind of circulatory system or blood-like juices, chances are good it'll have plenty of creatures whose sole desire in life is to suck the life blood out of someone else and make it their own!
In Earth medicine, leeches have long been used for a variety of purposes. So long as those purposes involved bloodletting! Medicinal leeches on Earth can chow down about 10cc of blood. Nowhere near enough for your needs. So you'll need to find some rather larger leeches!
Giant Leech, WorldAnvil
