One of my father's favorites:
There was a dog that needed to cross a river. He stood on the shore, puzzling over how he was going to do that. Along came a scorpion, who also happened to need to cross the river.
The scorpion said to the dog: "I have an idea. Since you can't see when you swim, how about I ride on your back, so I can tell you where to go? This way we can both cross the river"
The dog was suspicious: "That would be an fine plan, but, wouldn't you sting me?"
The scorpion: "If I stung you, I would drown, wouldn't I?"
With that reply, the dog agreed to the proposal. The scorpion climbed on the dog and they started swimming towards the other shore.
But half-way in the river, the dog suddenly felt a great pain on his neck.
"Why did you sting me? We are both going to die!"
"Sorry," said the scorpion as they both sank into the river, "I couldn't help it. It's just my nature"
