His references Capaldi. Well, here is either an example of Moffat being an arse and not holding together a decent plot (since there are a multitude of other things that the Doctor needs), or it's something to do with it being a [SPOILERS!!] thirteenth regeneration, therefore not natural. [/end spoilers!] This also plays into the part at the end when Capaldi remembers certain things, such as having 'new' kidneys (which means he remembers about regenerating or something because otherwise they wouldn't be 'new',) but not others, such as how to fly the TARDIS. All in all, The Day of the Doctor makes for an extremely interesting new series!