"Vague terror" is terror that has no clear cause; as such, it is all-encompassing.
Usually terror is directly caused by something. For example, someone might have a terror of heights, crowds, or spiders. In these situations, the source of one's terror is clear, and avoiding the trigger (heights, crowds, spiders) is generally easy to do.
If terror were to have a clear source, it could be easily defined (and therefore easily combatted). When terror is vague, however, it cannot be easily defined (and cannot be easily defeated). Therefore, "vague terror" is much worse.
I would love to help! Where is the sentence to this question?
<u><em>Answer</em></u>: "They saw the old cities,...lying children's delicate bones among the blowing lakes of grass."
<u><em>Explanation</em></u>: A metaphor doesn't use words such as "like" or "as". A metaphor states how it is. So take away any words that would compare the two things, get rid of "like" or "as".
I hope this helps. :)