Then, one of the computer scientists said "Here comes the conductor!" and they all ran into one of the the bathrooms. The mathematicians were puzzled. The conductor came aboard and said "tickets please" and got tickets from all the mathematicians. He went to the bathroom and knocked on the door and said "ticket please" and a ticket appeared under the door. The conductor took it and left. A few minutes later, all the computer scientists came out of the bathroom. The mathematicians felt really stupid.

So, on the way back from the convention, the mathematicians bought just one ticket for the whole group. They started snickering at the computer scientists, for they had no tickets amongst them. Then, the computer science lookout said "Conductor's coming!" and all the computer scientists ran into the first bathroom. All the mathematicians majors ran to another bathroom. Then, before the conductor came on board, one of the computer scientists left their bathroom, knocked on the other bathroom, and said "ticket please."