If you don't already know what a Therian is, you can find out here. In short, it's someone who thinks they are at least part animal. These people get paid to give blood, which then gets sold to 'good witches and wizards' for use in their spells.
"Our priests pray over the blood before it's shipped to your door for extra protection."
But they ARE BMM approved!. Scroll down and read the second complaint - "I am so sorry. I caught my three year old peeing in the blood container. I am so so embarrassed. Please accept my apologies. Theriantype.com is a wonderful company. I need to put this stuff on a much higher shelf. I took my son to the doctor, and apparently his father has some canine therian in him (we didn't know.) My kid was trying to mark his territory because he smelled another dog in the house. Again, so so sorry." O.o
Umm... I'm really not sure what you'd use blood from people who think they are animals for - is this an animal rights thing? Anyone?
[EDIT] More fool me. As it turns out, the site is part of an elaborate background to a novella, made by an author who is using the internet to create a kind of crossover for Really Keen Fans. It still scares me a little though because there are people out there who'd be into this.