The scorpion and the frog

A scorpion asked a frog for a ride across a river. The wary amphibian agreed, but only after the scorpion vowed not to sting him. Halfway across, however, the scorpion plunged his stinger into the frog, and the latter cried out, “Why?! Why?! Now we’ll both drown!”
The  scorpion  replied,  “I couldn’t help it. It’s my nature.”