"Huh?" Clara asks. She was too busy deep thought. Sometimes, if she concentrated deep enough on someone the Doctor had been with before, she could conjure up small glimpses of parts her echoes would see them. Of course it was never much, nor did it happen a lot but the occasional small glimpse. "I take it he hasn't explained the whole regeneration thing to you yet?" She asks, as Donna's words finally process in her mind and she gives up on trying to get a glimpse.