Sorry, I'm not into fiction...Your AI is failing you there. "The beast with two backs" is a euphemism for sexual intercourse popularized by the Bard of Avon. If copulating with a Seraphim, that "beast" would have five faces and four wings in addition to the two backs. Therin lies the humor.
The point was that the flood did not wipe out the angels, so there were still angels after the flood for Noah's descendants to shag with, and the Biblical account of Nephilim among the Canaanites confirms this as being canonical.
One notable euphemism for sexual intercourse popularized by Shakespeare is "making the beast with two backs." This phrase is used in the opening scene of Othello when Iago tells Desdemona's father, Brabantio, that his daughter and Othello are now "making the beast with two backs". This expression vividly describes the physical act of sexual intercourse.
Shakespeare appears to have borrowed this phrase from the French writer François Rabelais. Though it has entered common usage, it still retains its ability to provoke a sense of humor and perhaps a blush from a modern audience.
It's important to remember that Shakespeare's works are filled with various sexual euphemisms and innuendos, often used to create humor or convey specific meanings without explicit language. Other examples include "die" as a euphemism for orgasm and "nothing" as a term for the female genitalia.