A scorpion wanted to cross a river but could not swim, so he asked a fox to carry him across. The fox, demurred: You'll sting me. Not I, said the scorpion, for that would mean the death of me, too. Very well, hop on, said the fox.

Halfway across the river, the scorpion stung the fox with a mortal wound. As the river sucked them both down, the fox said, you promised! Why did you sting me?

I know, said the scorpion. But it is my nature.

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Crossposted, with comments, at firedoglake's Oxdown Express.