* HeyItsThatGuy: John Frobisher is played by '''[[Creator/PeterCapaldi PETER.]] [[Series/TheThickOfIt FUCKING.]] [[Creator/PeterCapaldi CAPALDI.]]'''
* WhatCouldHaveBeen: Martha Jones and Mickey Smith were supposed to appear in ''Children of Earth'', but Creator/FreemaAgyeman was [[Series/LawAndOrderUK busy]]. The two are [[WrittenInAbsence explained away as being on their honeymoon]] (though we don't know it's them married until ''Doctor Who'''s ''The End of Time'') and unable to help the team.