Madara "created" Black Zetsu (at least he thought he was doing so), but if Black Zetsu already existed, what made Madara "create" him, so to speak? I mean, he thought he was creating him, so how did he learn how to "create" him? How did Black Zetsu even get out of Madara's hand onto white Zetsu, if Black Zetsu wasn't created by Madara???