Continuity mistake: The baby gets into the fridge, which then closes - we see a closeup shot of the babyproofing clip shutting itself. Then when the mother sees the spilled milk and realises what's happened, there are a few shots of the fridge - in shots from the front the clip's open, and in shots from the side it's closed. When she goes to open the fridge it's open again - she even fiddles with it to give the appearance of undoing it before opening the fridge door.
Visible crew/equipment: When Sam tells the little girl to take her brother outside. The little girl runs out with her brother and Dean asks the little girl where Sam is, Dean runs to the Impala and grabs a shotgun. When Dean is running to the house, he runs on the lawn and you can see the shadow of the camera man running with Dean at the bottom of the screen.
Answer: Angels themselves may not have genitalia, but their vessels do. Nephilim occur when an angel in a vessel reproduces.
Greg Dwyer