Zombie walks have become relatively common in large cities, especially in North America, often becoming annual traditions, though some are also spontaneous "flash mob" events or performance art. Promoted primarily through word of mouth and online message boards, zombie walks are an underground activity. During the event participants are encouraged to remain in character as zombies and to communicate only in a manner consistent with zombie behavior. This may include grunting, groaning and slurred, moaning calls for 'brains'. Zombie behavior is a hot topic of debate. Purists who draw their definitions from the original Romero Living Dead films will claim that a zombie would never have the ability to call for 'brains' and furthermore that a zombie needs only living or freshly killed flesh for its sustenance, and not the brain in particular.
The complexity and purpose of some zombie walks have grown and changed with their popularity. An advanced technique to heighten interest and realism, some zombie mobs will "eat" victims to create new zombies, in sight of onlookers. The better coordinated zombie mobs will establish a route and an easily recognizable signal, so that other participants can plant themselves, appearing as an otherwise ordinary human, along the route in old, tearable clothes, and as the mob shambles along it can discover and devour new victims. As the zombies surround the new victim to loudly feed, concealing him or her from witnesses' view, they tear clothes and quickly apply makeup and fake blood, to create a new zombie, who then shambles along with the ever-expanding pack to find new victims. Some participants occasionally dress up as soldiers who are called in to contain the outbreak, or survivors who are trying to defend themselves from the onslaught of the zombie horde. Some events are staged as spoof political rallies organized "to raise awareness of zombie rights", with participants carrying placards. Many zombie walks have also been staged as "hunger marches" with the intent of raising awareness of world hunger and collecting items for food banks.