T-Rex: When you become a vampire you become undead. Even though your body has died and your heart no longer pumps and lungs no longer breathe, you live still. Your brain is fine. Your intelligence is unaffected. You have not suffered a death of self.
T-Rex: Pretty sweet deal, babes!
T-Rex: But what if that delicate process that turns you from mortal to vampire... failed? What if something in this turning went wrong, even briefly? We can suffocate to death in minutes, suffer brain damage in seconds. Suppose, during that transformation from a being who needs an active circulatory and respiratory system to survive to one who doesn't, there was a problem. Suppose your brain - everything that makes you YOU - died.
Utahraptor: Why, you'd be left with an undead body but a dead brain!
T-Rex: SOUND LIKE ANYONE YOU KNOW??
T-Rex: Utahraptor, I put to you that vampires and zombies ARE, IN FACT, THE SAME BEING. Zombies are merely FAILED VAMPIRES, the degenerate case of that transformation process!! The thirst for blood, without an intellect to restrain it and refine it, becomes a mindless hunger for flesh!
Utahraptor: Holy crap.
T-Rex: I KNOW. VAMPIRES JUST GOT AWESOME.
T-Rex: Y'ALL CAN THANK ME LATER
T-Rex: WITH, LIKE, LICENSING DEALS