To get rid of the annoying worm;
Spoiler
You have to keep diving out of his way when he attacks so that he bashes himself into the wall. You do this a certain amount of times and he dies. There is a sequence to it, but im afraid i cant remember it. I think it has been said in the games thread in the completed games forum.
Spoiler
Each time you try, you keep learning more and more of the sequence. There are 3 parts of the cave, and you have to be anywhere but where the worm strikes. Eventually the wall caves in on him and he dies.