Once it happens you can’t remember how you started out: innocent, barreling into the tunnel, shooting out at each station like a dolphin out of a dim green pool. Pneumatic doors inhale open, puff shut, lock with a solid thump. Up and down the line, fifty times a day, it’s a long slow song. You feel the rumble as much as hear it. In your dim green trance the words retain wonder: Vorsicht, Türe werden geschloßen. Caution, the doors are closing. Then the first time: someone decides darkness will answer, hides out in the tunnel, steps out in front of the train like he knows where he’s going, steps out at you, dying at you, knowing you can’t stop in time. Now each time the doors close, they seal you in. You are a human bullet shot into the tunnels, hoping no one will block the light far ahead, each station one minute’s reprieve.