Three lawyers and three engineers are traveling by train to a conference.
At the station, the three lawyers each buy tickets and watch as the three
engineers buy only a single ticket.

"How are three people going to travel on only one ticket?" asks a lawyer.

"Watch and you'll see," answers an engineer.

They all board the train. The lawyers take their respective seats but all
three engineers cram into a restroom and close the door behind them.
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 lawyers see this and agree that it is quite a clever idea so, after the
conference, they decide to copy the engineers on the return trip and save
some money (recognizing the engineers' superior intellect).

When they get to the station, they buy a single ticket for the return trip.
To their astonishment, the engineers don't buy a ticket at all.

"How are you going to travel without a ticket?" says one perplexed lawyer.

"Watch and you'll see," answers an engineer.

When they board the train the three lawyers cram into a restroom and the
three engineers cram into another one nearby.

The train departs.

Shortly afterward, one of the engineers leaves his restroom and walks over
to the restroom where the lawyers are hiding. He knocks on the door and
says, "Ticket, please."