The Train Compartment

[postman]

There were four people sitting in a train compartment: an old lady
who was knitting, a young woman who was reading a book, a lecturer
who was talking about his research, and his young student whom he
was taking to a conference, and who was listening to his lecturer and
taking down notes.

This situation continued for quite a while. The old lady knitting, the
young woman reading, the lecturer talking away, and the student
listening.

Then the train went into a tunnel, and the compartment was plunged
into darkness. No-one could see anything. Suddenly there came the
sound of a loud kiss, followed by a hearty slap. As the train came out
of the tunnel, eveyone was in the same position as they had been before.

Now the old lady thought that she knew what had happened. Good for
her, she thought, that young man has just kissed the girl, and she
slapped him.

The young woman thought that she knew what had happened. How
funny, she thought, the young man tried to kiss me, kissed the old
woman by mistake, and she gave him a slap.

The lecturer thought that he knew what had happened. It's not fair, he
thought, my student kissed that girl, and she slapped me by mistake.

But only the student really knew what had gone on. Under the cover of
the darkness, he had loudly kissed the back of his hand, then slapped
his lecturer and got away with it.