A biologist, a statistician, a mathematician and a computer scientist are on a photo-safari in africa. They drive out on the savannah in their jeep, stop and scout the horizon with their binoculars.
The biologist: "Look! There's a herd of zebras! And there, in the middle : A white zebra! It's fantastic! There are white zebra's! We'll be famous!"
The statistician: "It's not significant. We only know there's 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!"
