I just went back and watched that becoming epi, then I looked up on the net and it looks like what Spike did is called a sleeper hold, where an oppent puts pressure on the other opponents carotid, cutting off blood supply to the brain, which then leads you to pass out. So if Dru had the blood to her brain stopped then yeah she would pass out, but i kinda figured if a vampires heart doesn't beat then the blood supply does not run through the body (so how can you cut off the blood supply if the blood isn't even being pumped) and red blood cells carry oxygen (among other things) which vampires don't need........: erm : ok I'm getting a little confused because now everything sounds conflicted....