How do you kill a vampire in Supernatural?

Why is cutting off the head the method that works?

Because the show set out to make its vampires dangerous at arm's length. Nearly every defence older vampire fiction relies on is taken away here: a stake through the heart does not end one, and sunlight only hurts them, like a very bad burn. That leaves a hunter with a blade and the nerve to get close enough to use it, and turns every vampire fight into a physical, risky piece of work that has to be planned rather than rushed.

The rule also keeps the show honest about violence. A beheading is not a clean or distant kill, and the series rarely pretends it is. Making the most brutal method the dependable one forces each hunt to ask whether the thing in front of the brothers is still enough of a person that taking its head should cost them something. The Colt, the gun that can kill almost anything, is the rare exception, and the story treats it as a prize rather than a tool.

What does dead man's blood do to them?

It knocks them down without killing them. Blood from someone recently dead leaves a vampire weak and slow for a short time, which turns a fight a hunter would lose into one they can finish. It arrives with the vampires themselves in season 1, and it was a deliberate design choice: the season's production history records that the show's creator added it personally, alongside retractable fangs inspired by the rows of teeth in a shark.

The idea has a grim neatness the show never needs to spell out. Vampires live by taking blood from the living, and the one blood that sickens them belongs to someone already gone. It also gives hunting a texture of preparation, arrows soaked in it, a syringe kept ready, that a single magic weapon would not. A hunter who meets a nest without it is in serious trouble.

Can a vampire be turned back into a human?

Yes, but only early, and never cheaply. The cure is a remedy from an old hunting journal of the Campbell family, and it needs the blood of the vampire who did the turning. It works only if the person has not yet fed on human blood; after that first feed there is no way back. The show uses it on Dean Winchester himself in season 6, episode 5, so the price is shown on a character the audience knows well: the cure is painful, and it leaves whoever takes it sick for days.

The narrow window keeps the cure from making the hunt easy. It offers hope to the newly turned and nothing to the rest, so the old hard choice stays in place for nearly every vampire the brothers meet. What it adds is a question a hunter has to answer quickly: whether the creature in front of them was changed against their will last week or has been feeding for a century.

Where do the show's vampires come from?

From one ancestor. Season 6 brings in the Alpha Vampire, the first of his kind, from whom every vampire in the series descends, and gives him a maker of his own in Eve, the mother of all monsters, who stands behind the monster families as a whole. Vampires live in nests of eight to ten, bound to each other and, through the bloodline, to him. He appears in seasons 6, 7 and 12, and the last of those ends him: Sam Winchester kills him with the Colt.

That family tree is what makes the vampires feel like a society rather than a string of separate monsters. A bloodline with a single head gives the later seasons vampires with politics, from a rogue hunter working for the Alpha to the British Men of Letters' campaign to wipe out every nest in America. The werewolves get a matching line of descent, and a single root for each family becomes one of the show's main tools for turning monsters of the week into a mythology.