You lean one round of ammo up against the door. That'll let you know if anything comes by and opens the door.
You trudge off to the left and stop short when you see off in the dark, foggy distance four heavily armed men. As you stop short and draw your weapons, they do the same. Various shouts and queries from you get no reply. As you advance, it becomes apparent that the men are mimicking your every move.
When you get within 5 feet of them, you suddenly realize that someone went to all the trouble to place a mirror right across the channel. It's perfect, no smudges, no distortion. Must be quite valuable, if it were possible to remove it in one piece.
Suddenly, however, Ross's reflection (of its own accord) scowls, draws its gun, and fires it straight at the real Ross. The mirror shatters, revealing more of the endless corridor. Sitting among the shit and glass shards on the floor is a single spent shell casing.
Right after this happens, you all hear a small 'tink' noise from the junction you just passed, kind of like someone dropping a pen or a cigarette lighter on the floor.
What do, heroes?