In this place the youth felt that he was an ______. This forgotten part of the battleground was owned by the dead men, and he hurried, in the vague apprehension that one of the swollen forms would rise and tell him to ________."

I believe you're looking for the words 'invader' and 'begone', respectively. Here's the quote in full from chapter 8:

"In this place the youth felt that he was an invader. This forgotten part of the battle ground was owned by the dead men, and he hurried, in the vague apprehension that one of the swollen forms would rise and tell him to begone."