The Scorpion and the Frog

There was a scorpion and a frog that needed to get across a river.  The scorpion asked the frog if he would give him a ride on his back across the river since he could not swim.  The frog says "Ok I will give you a ride as long as you don't sting me" The scorpion says "why would I sting you?  It would kill us both!"  So the frog starts to swim across the river with the scorpion on his back.  About half way across the river the scorpion stings the frog.  The frog cries out "What have you done?!? You have killed us both!!"  The scorpion replies "I know but I could not help myself.  It is against my nature" as they both drown.