Saw

*Unmissable*

After you encounter your first minion, you will have to continue on through a door in the room (not the shotgun door... or the one the minion comes through). Progress through the hallway avoiding the glass on the floor and you will go through a shotgun door. Once in that area, there will be 3 rooms. The one in the middle will have a patient file and a nail for unlocking the first door. You must unlock that door to continue... it's a pretty simple mini-game.