Blood is a red fluid that transfers oxygen around the body. Vampires must drink blood of the living to stay alive. Fledglings must drink blood (or a blood substitute) or their mortal body will die, but when a fledgling drinks human blood he/she turns into a full fledged vampire. In Blood Drive it's revealed that Ethan has H-deficient blood, which means it's considered by vampires to be the best blood there is (because only one in a million people have it), thus making it taste and smell particularly delicious to vampires. In Re-Vamped, it's revealed that vampires and fledglings can suck the venom out of a human to prevent them from becoming a vampire, much like one can remove snake venom from a person's body.