A biologist, a statistician, a mathematician and a computer scientist are on a
photo-safari in Africa. They drive out on the savanna in their jeep, stop and
scout the horizon with their binoculars.

The biologist: Look! There is a herd of zebras! And there, in the middle, a
white zebra! It is fantastic! There are white zebras! We will be famous!

The statistician: It is not significant. We only know there is one white
zebra.

The mathematician: Actually, we only know there exists a zebra, which is white
on one side.

The computer scientist: Oh, no! A special case!