The metro car's dim lighting and the rhythmic clacking of the tracks fuel the passenger's dirty mind. They imagine the quiet, prim businessman in the corner, his crisp suit hiding a raging hard-on, or the young, innocent-looking student, her textbooks covering a desperate need for release. As the train pulls into the next station, the passenger's hand moves faster, their breath hitching as they approach the edge, ready to explode in a silent, secret climax.