You climb down onto the big gray stones that fill the space around and between the rails. It's hard to find your footing. You step onto the warm, well-worn metal of the rail. Once, you were in a physics class, and the instructor brought in a long, half-inch thick metal rod. To demonstrate the elasticity of the material, he held it at one end, slid it out of its plastic case, then ran his hand fast down the whole length of it. A faint thrumming filled the cinder block room. He did it again and again until the rod was singing, then screaming, like a clear light alarm. You can feel the faint vibration through the rubber soles of your shoes, and stumble toward the other tracks. The moment your body makes contact with the powered rail, you light up, and all of a sudden you... die?