Director George A. Romero (Night of the Living Dead) knows a thing or two about zombies. So it’s no surprise that Activision Publishing enlisted the horror director to appear as himself in the new Call of the Dead zombie level that gamers can download on Xbox Live starting May 3 . Actors Robert Englund (Nightmare on Elm Street), Sarah Michelle Gellar (The Grudge), Michael Rooker (The Walking Dead) and Danny Trejo (Machete) have joined Romero in the new undead level, which is part of the Call of Duty: Black Ops Escalation expansion pack . The zombie storyline was inspired by Romero, according to Mark Lamia, studio head of Treyarch. He said his Santa Monica-based team set out to create an exciting new zombie experience for fans of the genre that takes the gameplay to an “insane new level.” The story focuses on a shipwrecked crew of fearless explorers who are hopelessly stranded in a remote abandoned Siberian outpost. Their dream of discovering the true origins of the mysteri