New players begin the game as one of the three survivor classes; Military, Scientist or Civilian; or as a Zombie. Each side in the struggle has its own advantages and disadvantages. Survivors move twice as fast as low-level zombies and are able to employ various weapons and tools. Survivor characters can communicate with each other in-game via speech, radio broadcasting, graffiti and text messaging. They can also barricade building entrances, keeping zombies at bay. Zombies, often referred to as "zeds", are limited to using claws, teeth, and blunt melee weapons. However, they can self-revive with full hit points when killed, whereas a survivor needs another player to revive them after death if they do not wish to play as a zombie. Higher level zombies can communicate with each other via a crude form of zombie speech, as well as through various groaning noises and hand gestures. It is possible to switch sides in the conflict: a survivor character that is killed will rise up as a zombie, and zombie characters may be brought back to life by a survivor who has the relevant skills and items.