Ever since I started re-reading BtVS fanfic, I've been wondering about vampire physiology.

In episode 1x07 - "Angel", Giles said: "A vampire isn't a person at all. It may have the movements, the, the memories, even the personality of the person that it took over, but i-it's still a demon at the core, there is no halfway."

So, essentially, vampires are dead bodies taken over by a demon. Vampires don't breathe and have no heartbeat, therefore no blood circulating through their bodies.

So how does a vampire get an erection? Biology 1.01 has taught us that erections require for the male in question to have blood pumping through his body; blood that pools in the spongy body of the penis and stiffens it. No blood circulation equals no erection, and thus no spontaneous erections and, of course, no intercourse should be possible. The only explanation for Buffy and Spike "fucking the house down" I can come up with is that vampires might have the ability to consciously direct blood to certain parts of their bodies (or at least whatever liquid they have in their veins that does not congeal and flows without a muscle pumping it through the body). Which would mean for fanfic that Spike's erections would be deliberate and not induced by, for example, him smelling Buffy.

The second question concerns vampiric digestion. Evidently Spike likes to eat and drink human food - at least on occasion (for example hot chocolate with marshmallows, as seen in episode 3x08 - "Lovers' Walk"). No normal blood circulation means, however, that the internal organs in the vampire's body are inactive, although somehow the stomach has to work in a pretty specific way in order for the ingested blood to be introduced into the vampire's system. But human food? What happens to that? Do vampires who eat human food need to rid themselves regularly of what their system isn't equipped to handle? Something like owls or cats coughing up hairballs and small bones comes to mind. The whole idea sounds complicated and uncomfortable, and leads me to believe that the effort wouldn't be worth the taste (unless you're something like a bulimic vampire, of course).

So my conclusions are: a) Spike has total control over his erections, and b) Spike spends time crouched over the toilet whenever he ingests human food.

Peculiar.

Of course, we could also explain it all away with saying: "It's all demonic magic, of course!"

Whatever. I think I've spent more than enough time contemplating the state of Spike's erections. Eeep.