Urban Legends (Theodore von Karman)

Karman held a double position: professor at Aachen in Germany and lecturer at Cal tech in Pasadena. As an important aeronautical engineer, he was consulted to several airlines, and so he got free transportation whenever he found an unoccupied seat on the plane of one of these airlines. So he commuted more or less regularly between Aachen and Pasadena, and gave similar lectures at both places.

Once, he was somewhat tired when he arrived in Pasadena, but being a trooper, started lecturing. That was not so difficult anyway: he had the notes which he also used in Aachen. He talked, but as he looked around he had the impression that the faces in the audience looked more blank than usual.

And then he caught himself: he had been speaking in German! He became very upset. "You should have told me -- why did you not tell me?"

At length, one student spoke: "Don't be upset, Professor. You may speak German, you may speak English; we will understand just as much."

-- Karman himself liked to tell this story.