After you see the movie clip were you fight Ocelot of GRU for the first time, you will folo Sokolov to the bridge. You will see a short clip, then The Boss will throw you off the edge of the bridge. when you get done healing yourself it will give you the opportunity to look around. Look all the way to the left to see the bones of The Sorrow. This is one of the cobra's. This will be your only chance to see them.