Traditionally, zombies climb out of the grave, which clearly indicates they are undead.
Lately though, as in Zombieland and general Zombie Apocalypse mythology, they get bitten and afflicted with some sort of transforming virus and the next day they are a brain-eating zombie, with no real indication that they ever died.
Lately though, as in Zombieland and general Zombie Apocalypse mythology, they get bitten and afflicted with some sort of transforming virus and the next day they are a brain-eating zombie, with no real indication that they ever died.