My son is obsessed with vampires and acts like one. How do I fix this?

Ever since my son saw Twilight, he acts like a vampire. One day, his teacher called home because he likced a kids paper cut. And at home, he always tries biting the dog. Another time he brought home a friend and took out a giant pot, then he put water in the pot and told his friend to get in the pot. His friend sat in the pot and my son began running around him chanting "Ooo ha ha ha ooooo ha ha ha". I pulled him aside one day and told him vampires are bad and not real. He still doesn't realize it. What should I do?