Provenance - S1-E19
Audio problem: When Sarah goes to touch Evelyn's shoulder, you hear Sam's voice telling her to stop, except his mouth isn't moving at the time the phrase is being uttered. (00:23:50)
Provenance - S1-E19
Other mistake: In the scene where Sam, Dean and Sarah go to compare the painting to the earlier photo of it, Dean, noticing the changed position of the razor, says, "Jared, check it out." He is speaking to the character Sam. The actor's name is Jared. [Confirmed in cast interviews].
Answer: Angels themselves may not have genitalia, but their vessels do. Nephilim occur when an angel in a vessel reproduces.
Greg Dwyer