what she means:In Left 4 Dead 2, the intro sequence clearly shows the team of 4 fighting up "30 flights of goddamn stairs" infested with zombies. When they get to the top, the rescue helicopter is just leaving and they have to fight their way back down. My question is, when they see the zombies, how come they act like they don't know what zombies are. Rochelle says, "Holy shit... Zombies, they're real..." I mean, didn't you just kill like 30 floors worth of zombies? Also the stairs they take back down are not 30 flights of stairs and they even find a working elevator. Why didn't they just try the elevator in the first place? How could valve leave this gaping plothole unaddressed? Another thing is by the time of "The Passing", which takes place just after Dead Center, Bill is already dead. Bill died in the Sacrifice, which took place after everything that happened in left 4 dead 1, obviously. The thing is, the very first campaign of Left 4 Dead 1 takes place 2 weeks after the first infection. Everything in left 4 dead 1 had to take place during or before dead center, because if it didn't bill would still be alive in the passing. If you put all these facts together, it means that the intro to dead center must have been at the very least 2 weeks after the first infection. How did they not know about the zombies? They are two whole weeks into the infection for god's sake. And even then, this means that every campaign of left 4 dead 1 had to fit into the timeframe of dead center. This seems to suggest that left 4 dead 2's intro takes place even MORE time after the first infection. None of it adds up.