Vampires can't be real or they'd be everywhere — Laura McLay's ground-breaking research into vampire population dynamics demonstrate a dismal Mathusian character in vamp-growth that put the lie to the sucker:
This argument becomes even more overwhelming if you model a vampire population as a branching process or birth-death process and assume that each vampire in the population has probability Pj of producing j offspring (with j=0,1,2,… ). The vampire population would either explode or die out, depending on the expected number of offspring per vampire. But if you take into account the fact that vampires live many, many generations (they're virtually immortal) and may create thousands of offspring, the population explodes (if you assume that each vampire creates at least one vampire, on average, before it dies). With those numbers, vampires would not be living under the radar–they would be everywhere!
(Image: Vampires are real, Creative Commons Attribution-ShareAlike image from Eyelash_divided's Flickr stream)