One of my favorite tales:

A scorpion was walking along the bank of the river, wondering how to get to the other side.
Suddenly he saw a fox. He asked the fox to take him on his back across the river.
The fox said, "No. If I do that, you'll sting me and I'll drown."
The scorpion assured him, "If I did that, we'd both drown."
So the fox thought about it and finally agreed. So the scorpion climbed up on his back and the
fox began to swim. But halfway across the river, the scorpion stung him.
As the poison filled his veins, the fox turned to the scorpion and said,
"Why did you do that? Now you'll drown too."
"I couldn't help it," said the scorpion. "It's my nature."