The Hospital

The Hospital is the fourth chapter of the first campaign, No Mercy. In this level, the Survivors discover that the hospital is overrun and the patients and staff are infected. The Survivors must travel up flights of stairs, through medical offices, and past the emergency rooms while fighting off the hordes of Infected. The Survivors soon find an elevator, the only way up to the roof, where the helicopter pilot will come to rescue them. Calling the elevator will signal a Horde, which the Survivors must hold off as they wait for the elevator. It should be noted that Zombies can drop from the ceiling and may come through the walls beside the elevator. There is a brief time at which the Survivors may rest in the elevator before they exit onto a windy construction area of the hospital. Carefully navigating the treacherous area, the Survivors finally make it to the safehouse and take one step closer to salvation.

Glitches

 * After the battle with the horde at the elevator, if a Survivor manages to become incapacitated inside the elevator (due to a rogue zombie, hunter, or even a Witch!) and is revived once the elevator has been activated, they are left behind - the elevator will rise but they will not. They will also be unable to leave the elevator shaft, and will be easy prey to any other infected.
 * Also throwing a propane tank or oxygen tank at a survivor in the lift will incapacitate them and will cause them to fall through the floor of the lift leaving them incapacitated at the bottom of the lift shaft.
 * It is possible to pull a Survivor out of the elevator just as the doors are closing (as a Smoker), leaving him/her at your mercy, so to speak.


 * There is a glitch in this level in versus where any of the special infected except the tank can run ahead in the level to the top of the elevator shaft and repeatedly melee the trailer in front of the elevator, eventually pushing it in front of the doors and trapping the survivors when they reach the top. It is considered a cheap move to use, as the survivors can only move it if a Special Infected melees it first, or if a boomer explodes near it, which gets the movement started. The reason for this is probably the move able physics objects that are included via Havok Physics Engine.
 * Only Special Infected (and explosions) can start the object moving, though Survivors can continue movement once it is started.


 * The above glitch also works with the forklift in the same level, it is most useful to put the forklift in the doorway left and then right of the doorway leading from the elevator door, on the top level of the hospital (by putting it in a doorway you can't jump onto and over the forklift and the only way around is on the outside where you can claw the Survivors off the roof).

Easter Eggs

 * In several of the Examining rooms there is an x-ray of a hand with four fingers, which is a reference to the cover of the game.
 * The second part of the level takes place on the 28th floor of the hospital, likely a reference to popular zombie movie 28 Days Later.
 * While playing as the Infected in versus mode, once the survivors have activated the elevator, wait inside the elevator and the floor number won't change. It will continue to say "04," in reference to the game's title.
 * In the chapter's starting safe room, there is some Graffiti on the wall, one area of which will say that "I killed..." some number of zombies, and the last number says 53,595, which is a reference to the Zombie Genocidist achievement.