In the cramped, dimly lit train toilet, a woman stands, legs wide, her back against the door. She's wearing a short skirt, no panties, her pussy exposed to the cool air. She slides a finger in, then another, her hips moving in a slow grind. The train's motion rocks her, intensifying the sensation. She adds a third finger, her breaths coming in short gasps. Just as she's about to come, the door handle jiggles, a voice on the other side asking if someone's in there. She freezes, then grins, inviting the intrusion.