I'm actually on the fence about vampires detecting Clark's not human. They can certainly identify other demons -- Spike knew Tara *wasn't* a demon in Buffy. (Remember when he slugged her to prove his point?) Not sure what the canon explanation was for how he knew, but he knew. Given close proximity, I dunno what they'd make of Clark or if Kyptonians smell different than humans -- haven't decided yet which way I'm going to go, if it even matters.
OTOH, it serves my purposes in a scene coming up in the story for vampires NOT to be able to identify a Kryptonian immediately. *grin* (Though the vampires in question are dumb fledgelings.)
One other thing that occurred to me is that Clark should be able to identify a vampire a mile away if he's actually looking for one. No beating heart. That's probably not occurred to anyone yet; he's so out of his depth and the Scoobies haven't fully grasped the level of his abilities yet.
