play. According to Guillaume, the team realized this potential when they implemented the lock-pick feature (when players must be aware of their surroundings while trying to unlock a door). To further immerse players in the game, the voice of the Prepper is channeled through the GamePad's speakers and players need to read text with the pad; since the GamePad is a real-world object, the experience is more intimate. The pad displayed most crucial information to the player, and the game did not have a user interface. ZombiU was designed as a realistic zombie game. Fear was the game's core emotion and it should be played slowly, similar to some classic horror games. According to game director Jean-Phillipe Caro, players will do badly if they try to play it as a fast-paced action shooter like Call of Duty and ignore the GamePad. A prominent game mechanic is the permadeath system, intended to increase its tension. With the system, the game featured several survivors instead of a hero character. Its narrative was designed to rely on environmental storytelling rather than cutscenes, and players would understand the story through the game experience. The team introduced a persistent level design, in which when players continue playing after their initial survivor is killed. Action by the previous survivor will still affect the game's world; previously-killed zombies will not re-spawn. The permadeath system was debated, with concerns about loading times and backtracking. To ensure that the game's narrative would continue after a player-controlled character died, the survivors were not voiced to avoid narrative dissonance; this made the player, not the survivors, the protagonist. Although Shrager was relieved when the central character was dropped, writing the game was the "toughest challenge" she had ever faced in games. Since survivors can die anywhere in the game, linking the story became difficult. The team introduced the Prepper, an important character who communicates with the survivors by radio to link them and advance the narrative. During development, the permadeath concept was nearly removed. A core team goal was a game which was difficult but fair, inspired by difficult games such as Dark Souls and Demon's Souls. The permadeath system ensured that players are often challenged, since every zombie can be a deadly threat. It fit the game's survival theme, giving players an incentive to continue. The game was designed for players to learn by experience, slowly improving their skill. The