Lawyers and engineers

Three lawyers and three engineers are traveling by train to a conference. At the station, each of the three lawyers buys a ticket while the three engineers buy only one ticket.
“How can the three of you travel on one ticket?” asks a lawyer.

“Watch and you’ll see,” answers an engineer.
Aboard the train the lawyers take their respective seats while all three engineers cram into the restroom and squeeze the door closed behind them.
When the conductor comes around collecting tickets, he knocks on the restroom door and says, “Ticket, please.” The door opens a crack and a single arm emerges with a ticket in hand. The conductor takes it and moves on.
The lawyers are impressed with this clever idea. One the way home from the conference, they decide to copy the engineers’ technique. At the station, they buy a single ticket for their return trip. To their astonishment, the engineers don’t buy a ticket at all!
“How in the hell are you going to pull this off?” asks a lawyer.
“Watch and you’ll see,” answers an engineer.
They board the train. The three lawyers cram into one restroom and the three engineers cram into the other restroom.
Shortly after the train departs, one of the engineers leaves his restroom and knocks on the other restroom door. “Ticket, please!”