The single exit in the room lead to a hallway.  I was made out of the same seamless sandstone.  The room had been at a dead end so there was only one way to go.  It also made it impossible for someone to walk past the door.  The same invisible light source was there and the end of the hallway couldn't be seen.  Further along the hallway it became dark and impossible to see what was ahead.  As Tris stands in the room a strange feeling would start to come over it.  It was as if someone was watching him, and not one of the two people he could see in the room.  The unseen eyes seem to be fixed on and his movements.  It was like knowing a snake was hidden in the room somewhere and it just saw him as a simple rabbit.  Maybe the room wasn't so safe.