Speaking to Box Office Magazine, Bill briefly mentioned Rob working with David Cronenberg and how he kept the birth scene PG-13:
BOM: We interviewed Robert Pattinson a while back and he said the only other director he could imagine handling the blood of Breaking Dawn was David Cronenberg [The Fly, Naked Lunch].Click HERE to read more!
BC: And then he went to work for him! [In 2012's Cosmopolis] But I know what he means because it is very, very intense in the last part—it's almost like a horror movie. And he's certainly delivered the most intense images in the last decade or so. I tried to get my Cronenberg on a little bit and I think within the confines of a PG-13 rating, I think we've got something that's pretty powerful.
Bill comments more on Breaking Dawn and being inside the wolf brain. *cries*