Well, this might be a bummer to some, I don't tend to consider standard biology or physics when thinking about vampires. At the end of the day, they were reanimated by supernatural means, so I try to to think about in a non-magical way. When I do, I can't help but think about Angel and Spike and all the talk about how their hearts don't beat etc, and I keep wondering why we don't see post mordem lividity, or what's it's like to have sex with someone who is room temperature.
![Wink ;)](http://www.dsboards.com/SMF/Smileys/classic/wink.gif)
It gets in the way of my suspension of disbelief, so I tend to try to ignore that stuff.
Now, with Chelsea Quinn Yarbro's vampires and ghouls, it's a lot more straightforward and if I may say a little more like the ideas presented in DS where there is something in the blood that changes its chemistry. A cell or virus, that, with a sufficient buildup, upon the victim's death, causes the body to reanimate, have an extreme photosenitivity and require blood as sustanance. Though there is still a very definitely a supernatural element as in her world the vampires do have a definite and necessary connection to their native earth.