* HeyItsThatGuy: John Frobisher is played by '''[[Creator/PeterCapaldi PETER.]] [[Series/TheThickOfIt FUCKING.]] [[Creator/PeterCapaldi CAPALDI.]]''' You might know him better as [[Recap/DoctorWhoS30E2TheFiresOfPompeii Lobus Caecilius]] or [[Recap/DoctorWho2013CSTheTimeOfTheDoctor the Twelfth Doctor]].
* WhatCouldHaveBeen: Martha Jones and Mickey Smith were supposed to appear in ''Children of Earth'', but Creator/FreemaAgyeman was [[Series/LawAndOrderUK busy]], as was Noel Clarke for a film shoot. 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''- we are led to think it was [[Recap/DoctorWhoS29E13LastOfTheTimeLords Tom Milligan]] up to the reveal that [[PairTheSpares Mickey really married Martha]]) and unable to help the team.