It is POSSIBLE that there was an omission in Genesis 4:1. This interpretation from the aramaic targum DOES seem to fit. It is apocryphal, so I can not attest 100% that this is true, but I put this here as something to consider. The concept of Eve being seduced and impregnated by the devil is confirmed in another apocryphal work, the protevangelion where Joseph says "Is not the history of Adam exactly accomplished in me?" referring to how Mary was pregnant without Joseph consummating with her.
Should this serpent seedline idea be true, it would explain the big reptilian conspiracy theory that is never taken seriously. There could be a race of people on this earth who truly are descendants of the serpent, and are serpentine or "reptilian." The Bible does say God will put enmity between the woman's seed, and the serpent's seed. It does seem to make sense.
The secret password of a master mason is tubal cain, a descendant of cain from the Bible. This is probably not a coincidence.