Continuity mistake: When there are zombies in the lift in the later stages of the game, if you clear it out then close and open the door, the lift will fill again before it has time to visit another floor.
Continuity mistake: At the beginning of the game, during the photography section on the helicopter, if you look closely at the woman on the warehouse roof who gets killed, you'll notice that's it's actually Michelle, a survivor you'll encounter later.