Chapter 7
1 And all the others together with them took unto themselves wives, and each chose for himself one,
and they began to go in unto them and to defile themselves with them, and they taught them charms
2 and enchantments, and the cutting of roots, and made them acquainted with plants. And they
3 became pregnant, and they bare great giants, whose height was three thousand ells: Who consumed
4 all the acquisitions of men. And when men could no longer sustain them, the giants turned against
 

5 them and devoured mankind. And they began to sin against birds, and beasts, and reptiles, and
 
6 fish, and to devour one another's flesh, and drink the blood. Then the earth laid accusation against the lawless ones.
 

On a parchment fragment 4Q201(En ara) copied ca. 200-150 B.C.E. found at Qumrum:  Other texts

13. [They (the leaders) and all ... of them took for themselves] wives from all that they chose and [they began to cohabit with them and to defile themselves with them]; and to teach them sorcery and [spells and the cutting of roots; and to acquaint them with herbs.] And they become pregnant by them and bo[re (great) giants three thousand cubits high ...]
     - Book of Enoch (from Translation by J. C. Greenfield

"Later Jewish tradition has it that their seduction was at least partly their own fault since they had taught the girls the art of cosmetics, and so had begun the awful progress of mankind to degeneracy and sexual abandon. More important, 'they taught them charms and enchantments, the cutting of roots, and make them acquainted with plants..." (Enoch 7:1ff)."
     - John M. Allegro, The Sacred Mushroom and the Cross

"The Hebrew word for giants (nephilum) literally means the fallen-down-ones because these tall celestial beings fell from the sky. Their half-breed progeny and their descendants are often mentioned in the early books of the Old Testament until the last of them were finally killed off. They were known as the Rephaim [Hebrew for 'phantoms'], Emim, Anakim, Horim, Avim, and Zamzummim. Some scholars speculate that this tradition of giants born from the union of gods and humans formed the basis for the demigod of Greek mythology."
     - Raymond E. Fowler, The Watchers