If we understand the “zombie movie” as a particular set of plot beats and characters, George A. Romero’s films are what brought that to the mainstream. There’s a mysterious disease, followed by lots of killing and running from zombies, then—in Dawn of the Dead (1978) and Day of the Dead (1985), at least—some number of our heroes escape by helicopter. Valve’s Left 4 Dead series ends up making this into a bit of a joke—each campaign is advertised with a movie poster, and ends with the players making their way to a vehicular rescue before they’re dropped into the next…