Chaos engulfs the streets of Philadelphia while Brad Pitt's Gerry Lane plays an innocent game with his kids in the latest clip from World War Z. While we still don't get a clear picture of how this zombie apocalypse starts, it's quite apparent that this epidemic spreads at a massive rate, with an annoying traffic jam turning into a life-or-death scenario. Find out more when director Marc Forster's adaptation of the Max Brooks novel hits theaters June 21.