Write about a train and its cargo or passengers.
The carriage was almost empty except for a man sitting alone at the front staring out the window. She could see his face clearly in the glass and inadvertently made eye contact with his reflection. He did not look away. She quickly opened her phone. Should she take a photo? Well you never know what might happen. He could be a mugger, a stalker, a rapist or even a murderer. He could also just be someone on his way home. She stood up at her stop. He watched her leave and unexpectedly squeezed through the closing doors right behind her.