While the dream sequence in the Book of Giants gets most of the attention, the scroll also describes something the Watchers tradition in 1 Enoch only mentions in passing: the Nephilim turned on each other.
The fragments describe the giants engaging in terrible violence, not just against humanity, but against one another. They slaughter animals, devour flesh, and drink blood. The earth itself cries out against them. The text echoes (Genesis 6:11-12): "The earth was corrupt before God, and the earth was filled with violence." But the Book of Giants makes the source of that violence specific. It was the offspring of the Watchers, half-angel and half-human, who were tearing the world apart.
One fragment describes Gilgamesh, yes, the famous Mesopotamian hero appears by name in this Jewish text, as one of the giants. Another fragment refers to monsters and creatures that seem to be the twisted offspring of the giants' own unnatural unions. The corruption spreads like a disease. The mingling of heavenly and earthly flesh produces not just violence but biological chaos, creatures that should not exist, hybrids that violate the created order.
The theological point is sharp. The Watchers did not simply break a rule. They corrupted the fundamental structure of creation. Their children, the Nephilim, embody that corruption in flesh and blood. The flood is not divine punishment in the punitive sense, it is a reset. God must wipe the slate clean because the boundary between heaven and earth has been so thoroughly violated that the world itself has become unsustainable. The Book of Giants makes the flood feel not arbitrary but inevitable.