LAS VEGAS, Nev. – Actor-producer Brad Pitt made an unannounced appearance at the annual CinemaCon convention in Las Vegas to show off material from his upcoming apocalyptic epic, “World War Z.”

“Listen, five years ago, I knew absolutely nothing about a zombie; today, I consider myself an expert,” Pitt said, smiling for a packed house of surprised theatre owners at Caesars Palace on Monday night. “This whole thing started because I just wanted to do a film that my boys could see before they turned 18 — one that they would like, anyways. And they love a zombie.” The 49-year-old Pitt and partner Angelina Jolie have six children, including three sons.

“So, we settled on this book, Max Brooks’ book, called ‘World War Z,’” Pitt continued. “We were faced with two Herculean challenges: How do we keep the global, spectacular, dynamic scope of the book and how do we originate a genre that’s been done quite often and really, really well? What you’re about to see is our answer to those two questions.”

A 3-D version of the film’s trailer was shown, along with 2-D versions of frantic and frightening stand-alone set pieces from the movie, which were perhaps best described as “The Running Dead.”

“World War Z” hits theatres on June 21.