Hopefully not Fallen Angels.
To clarify what I mean...
The Bible is full of opposites. If Mary could conceive that which is good without intercourse, perhaps a woman could conceive that which is wicked in a similar way. The Occult World is always trying to call some Fallen Angel into the Womb of a Woman during certain rituals. The movie Eyes Wide Shut has some of that in it.
Some believe in Alien Abductions by which 'things are done' to the victim's reproductive organs.
How exactly does the 'mingling of Seed' happen in Daniel?
Daniel 2:43 - "And whereas thou sawest iron mixed with miry clay, they shall mingle themselves with the seed of men: but they shall not cleave one to another, even as iron is not mixed with clay."
I believe the 'they' mentioned above are the Sons of God back at their old ways. What happened in the Days of Noe is going to happen again. Hybrid Humans.