I was on the train this morning, headed for an appointment downtown. A woman ran up to the train, hoping to board as the doors closed. She failed, but managed to get a finger between the doors; I expect she thought the doors would spring open, due to intervention from some sort of finger-in-the-door sensor.
The door stayed closed. I began to wonder what would happen if the train began to roll. It might be that some helpful electronic sentinel might croon through the platform speaker in it's typical Deanna Troi voice, "Attention... warning... the train is about to leave... please remove all appendages from the door, and await the next train..."
No voice, but the train didn't start to roll, lucky for the lady. She managed to extract her finger intact.
I'm glad it didn't come down to her gnawing it off.