A pair of university students in Frankfurt decided to conduct a behavioral study. They found two phone booths in close proximity to each other near the city center, and they posted official-looking signs on each; one said "Men only" and the other "Women only." For days, they studied the booths and learned that the people quite readily obeyed the signs and used the appropriate booth for their gender. They found that people would queue up at the correct booth, even if the other was vacant. It wasn't until the fifth day of the study that a woman dared to enter the "Men only" telephone booth.
She was from Paris.