Riniel Jasmina wrote:
The reason the Israelites were forbidden to eat the blood of a creature was because it was considered the life force of the animal.  That's where the idea of vampires come from.
(Sorry, I'm somewhat of a pedant; since I have other comments to make on this topic, I feel somewhat compelled to address these.) It wasn't just the Israelites (the Bible tells us) who were forbidden to eat blood; I believe the ban on eating blood dates to the Noahic expansion of the diet to include animals, which is why the Council of Jerusalem laid abstention from blood as one of the only obligations on Gentile Christians. Also, my reading of "the life is in the blood" isn't so much that the blood was considered to 
be the "life force" of the animal, but that it 
contained it, so that by spilling blood one was taking life. As the giving and taking of life was God's sole prerogative, it took a divine grant to permit us to shed the blood of animals, and consuming it (to try to lengthen our own lives) or shedding human blood continued to be forbidden.
I'm somewhat doubtful about this being the origin of the idea of vampires, since "the life is in the blood" and the prohibition on eating blood dates to (like I said) Noah, while I seem to recall reading something about the origin of the vampire legend being somewhere in Europe in the medieval era at the earliest.
Riniel Jasmina wrote:
It's perfectly normal for an animal to eat the blood of it's prey but the evil life force of an evil creature would probably have side affects, health aside.
The thing is, for something to be truly 
evil in 
itself---as opposed to the tool of evil or "an evil" to punish covenant-breakers (I've been reading Deuteronomy recently; being overrun by wild animals is one of the covenant curses that God promised would come if they failed to keep the covenant)---it seems to me it has to be intelligent, at 
least an "apex predator" if not human-level with a moral sense. And many cultures (I'm not sure precisely what the Old Testament law had to say) forbade the eating of 
any predator. 
Also, evil is often associated with corruption (a recently-popular, particularly egregious example is zombies); people usually want to avoid eating anything that's even slightly tainted by corruption (such as mold or rot). Just as you might eat slightly moldy bread if you had nothing else to eat, an evil creature might serve as food as a last resort, but it'd be something you'd 
really want to avoid.
I also note (for comparison, as "how this author handled a related point") that (if I recall correctly) in 
The Lord of the Rings nothing grew from the place where they buried or burned (whichever it was ...) the Nazgûl's winged mount.