"...I don't have any darkness in me now, so maybe that explains that. If losing your heart's supposed to create a Nobody and I didn't..." It was the only thing that made sense to him. And after that first forceful separation, his heart really didn't have any darkness. If it could happen to girls, why not guys too?

But that second bit of info from Roxas draws his attention. "Body snatching? So his Heartless could... take someone over?"