The clicking sound vanishes as you enter the next train car. It's dimly lit, unusually large, and sparsely decorated. Just rows and rows of dull gray seats. As you make your way through the cabin, a flash of red against the gray catches your eye. A ragged piece of cloth lies discarded between two of the seats. Looking closer, you see a red cross painted on a white background. Maybe a flag of some sort?
You continue after a moment, and soon find yourself at the door to the next cart. Locked again, but this time there's no room for a key. Glancing around, you notice there seems to be a motion activated sensor at the very top of the door. It's too tall for you to reach, even when you jump. Annoyed, you slump into the nearest seat and consider your next move.
It's then that you notice a large hole in the floor of the car, leading into pitch black nothingness. It's just wide enough for you to slip through, if you're so inclined. Otherwise, you can either try to think of a solution, or retreat back to the previous carts.

You wander through the cart as you try to think of a way to pass through, settling beside the white cloth. Absentmindedly you fiddle with the frayed material, and realize that it's much longer than you thought - not so much a flag as a banner. An idea springs to mind, and you approach the door with cloth in hand. You leap upwards again, unfurling the banner as you do. It takes a couple tries, but eventually the sensor lets out an approving beep and the doors slide open. You saunter into the next car, pleased with your success.