Am I the only one who sees the fatal flaw in this? I don't want to sound like every other nonbeliever here, and I'm certainly not saying I'm an expert on breasts or anything. However, the amount of muscle it would take to make them move in the way that they do in that video is unrealistic, especially with the (alleged) size of her breasts. Breast tissue is not muscle, and with the size of her breasts, there's no way that they'd move that much with flexing.
Now, I'm not saying all of this to make it seem like they can't be real. I just don't think they're moving like that because of flexing. Maybe some other theories out there?