The teacher asks the students: "What is a turbot?"

Fritzchen answers: "A very flat fish."

Teacher: "And why is it so flat?"

Fritzchen: "Because it had sex with a whale."

Outraged, the teacher takes Fritzchen to the principal and tells him the whole story.

The principal asks: "Why are you doing such nonsense?"

Fritzchen: "It's not my fault that the teacher asks such stupid questions, she should have asked why the frog has such big eyes."

Principal: "Why does it have such big eyes?"

Fritzchen: "Well, he saw the whole thing!"