1-2-3, A-B-C.

Scorpion needs a ride across a river, asks a frog for same.

Frog says, "but you're a scorpion, you'll sting me and I'll die.'

Scorpion says, "No, no, no. If I did that, you'd die, but I would drown."

Frog figures this makes sense and tells the scorpion to hop on his back.

Halfway across the river, frog feels an excruciating pain. Turns, looks at the scorpion and says, "Now we're both dead. Why on earth would you sting me?"

Scorpion says, "Can't help it, I'm a scorpion. It's what we do."