World War Z continues the trend of making zombies more than just shambling, shuffling biters. As we said in our review of the film, they move fast and swarm like deadly, human-sized fire ants. To achieve that effect, it would have been too time intensive to animate each and every one. Instead, as Wired explains, the visual effects firm Motion Picture Company picked up on an idea that WETA used in The Two Towers: make each zombie an individual "agent" with its own goals and and behaviors and then set it loose on the world. MPC added an additional layer of more advanced artificial intelligence called "Alice," as this Wired video details. Once Alice set up the shots, animators added in additional details by hand, and the end result is a terrifyingly realistic wave of the undead.