Many Nephilim, one ?

for some reason since childhood I've been curious about the Nephilim. It's written so matter of fact like in the scripture. 

Genesis 6:4
"The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown."

Numbers 13:33
"There also we saw the Nephilim (the sons of Anak are part of the Nephilim); and we became like grasshoppers in our own sight, and so we were in their sight."

"The Emim dwelt therein in times past, a people great, and many, and tall, as the Anakim; which also were accounted giants, as the Anakim; but the Moabites called them Emims. (Deuteronomy 2:10, 11)."

Deuteronomy 3:11 describes one of these giants:

"For only Og king of Bashan remained of the remnant of giants: behold, his bedstead was a bedstead of iron; is it not in Rabbath of the children of Ammon? Nine cubits was the length thereof and four cubits the breadth of it, after the cubit of a man."