There is clearly a lot that we do not know. If you look at it all like a detective then I think we have some clues as to what has been going on with Satan regarding this earth. Basically he took over the earth prior to the flood, with his demon hordes. As the bible puts it, "they took wives for themselves, namely all whom they chose." I think the "all whom they chose" is very telling. What were they up to? That is the question that lingers to me. I think there were two primary things. They desired to be worshiped, and they were trying to stop the birth of the messiah.
Well, they could not stop the Messiah, but they still want to be worshiped.
So look at what we know and what we don't know, and when you put those two things together we have clues that you would not have otherwise. The bible says almost nothing about the pre-flood world, but even so, it still says a lot. In the Insight book the wording about the Demon's materializing bodies is curious. It says "apparently" they cannot. But the truth is we don't know what they can or cannot do, all we really know is they didn't (can't) do what they did on the scale they did it, before the flood. Does that mean they cannot materialize bodies and father children, or does it just mean they cannot do it on the scale they did it before the flood, and or perhaps they test how far they can go, testing what Jehovah will let them get away with, knowing to a large extent what they can get away with.
When you look the account of the 12 spies, it's pretty interesting what Caleb and Joshua say and again what they did not say. Not once do Joshua or Caleb say that there were not Nephilim in the land of Canaan, and in fact "Goliath" was a family name and they were at least three giants. No rather Caleb and Joshua say, "Jehovah will deliver the inhabitants into their hands." And something to the effect of, "They cannot stand against us we have Jehovah on our side." (I forget what book this is all in, I can find it and read it recently in the last couple months.) In any case they never said that there were not giants in the land.
Then when we look at the command Jehovah gave the Israelite's to "kill every man woman child and beast", in certain areas, perhaps that was because the demons were doing what they had done prior to the flood. This is in fact the theory Steve Quayle has and I think it makes sense.
Steve Quayle also talks about the many finds of giant skeleton's that have been found all over North America that the covered up by Smithsonian, all the stories of giants in culture from all over the world. In one of his interviews he talks about a US vet whose company ran across a very large giant that a squad ran across in the mountains of Afghanistan, that killed the whole squad, and they sent in a large assault and killed it, and had to bring in a large cargo helicopter to remove it from the scene. The most interesting part of this story is I started to relate something about this to a business associate, and before I had even started, he tells me a very similar story of a classmate of his, whose now in MARSOC, (Marine Corp spec-ops), that ran across and killed a giant in you guess it Afghanistan.