Since the last post mentioned about vampires, allow me to convince you that vampires may exist.
Think about it, if Man could evolve over time to better adapt to their environment and circumstances, why couldn't supernatural creatures, especially one like the vampires (they do still possess a human brain after all). It is, in fact, very viable that a small population of vampires exist.
Vampires are violent creatures and would likely fight amongst themselves. Also, if the group gets too large, human detection would be inevitable. How can these vampires then stay alive without raising alarm? We need to lay down some ground assumptions that I have:
1. Like humans, they adapt.
2. Vampires learn to control.
3. Blood is not necessary in large quantities. You don't need to eat a cow every day to stay alive. Neither do they need to drink galleons of blood.
It is definitely sustainable for the small population of vampires to survive. Take out the crap you read from Twilight; vampires don't have sex and re-produce. These X number of vampires can get the amount of blood they require via the following ways:
1. Stealing blood from blood banks, hospitals and morgues. Vampires are said to have breakneck speed, so what can stop them?
2. Human blood with "mysterious disappearances".
3. Hunting wildlife. More and more people are becoming vegetarian, by choice. So can vampires.
All these, is based on the assumption, that vampires did truly existed.
Shoot, score, smile.