Shortly after the train has departed, the conductor comes around collecting tickets. He knocks on the restroom door and says, "ticket, please." The door opens just a crack and a single arm emerges with a ticket in hand. The conductor takes it and moves on.


The accountants saw this and agreed it was quite a clever idea. So after the conference, the accountants decide to copy the engineers on the return trip and save some money (being clever with money, and all!) When they get to the station they buy a single ticket for the return trip.