scorpion and the frog

A scorpion wishes to cross the river and asks the frog could he ride across on his back. The frog is hesitant as he believes the scorpion will sting him, but the scorpion explains that if he did they would both drown. The frog agrees and takes the scorpion across the river. While half way across the frog feels the scorpion sting him. The dying frog asks the scorpion why he’d do this and the scorpion explains that he couldn’t help it, as it is in his nature.