This is, again, something Tedd was able to determine SOMEHOW.
Granted, there’s an explanation for how he’d know (aside from “he’s a scientist. He scienced it”), but for now, I’m going with a solid SOMEHOW.
As for why and how the transformation works that way, I’m going to go with a solid “because I said so”. Also “because science”. And “a wizard did it”. And “insert technobabble here”.