How do you kill the sorrwow in Metal Gear Solid three snake eater

You cannot kill The Sorrow in Metal Gear Solid 3: Snake Eater as he is already dead. To end the boss battle, you must walk to the end of the river while avoiding the ghosts of the people you have killed. When you touch The Sorrow's skeleton, you will die. At this point, you must open the Item menu and select the Revival Pill, which will end the battle.