A scorpion on a journey was stopped in his travels by a river. The river was wide and swift, and the scorpion could find no way to cross. He finally saw a frog sitting in the rushes by the bank and said, “Friend Frog, will you do me a kindness and let me ride across the river upon your back?”
The Frog said, “How do I know that if I let you on my back, you will not sting me?”
“Because,” the scorpion replied, “If I sting you, then I would die too, for I cannot swim.”
So the frog agreed. The scorpion crawled onto the frog’s back, and the frog slid into the river. Halfway across the river, the frog suddenly felt a sharp sting in his back and, out of the corner of his eye, saw the scorpion removing his stinger. A deadening numbness began to creep into his limbs.
“You fool!” croaked the frog, “Now we shall both die! Why on earth did you do that?”
The scorpion shrugged, “I could not help myself. It is my nature.”
The Deaf Dog's Almanack 