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* ActingForTwo:
** Old Kazran and Kazran's dad are both played by Creator/MichaelGambon. Leads to a heartbreaking moment when young Kazran calls his old self "dad?"
** Likewise, Young Benjamin and the unnamed younger Pettigrew in the present are both played by Bailey Pepper.
* AuthorPhobia: The flying shark was inspired by Creator/StevenMoffat's childhood fear of sharks rising out of water.
* TheCastShowoff: Music/KatherineJenkins, better known for being a GlamorousWartimeSinger, plays Abigail. Of course she ends up singing.
* CompletelyDifferentTitle: The French title is "Le Fantôme des Noëls passés" (The Ghost of Christmasses Past).
* CreatorBacklash: Michael Gambon was apparently unhappy with his performance.
* DevelopmentGag: Eleven produces a picture of himself with Einstein towards the beginning of the special. Creator/MattSmith wrote fanfiction about the Doctor meeting Einstein after being cast to prepare himself for the role.
* StuntDouble: The Doctor's entrance via the chimney was done by a stuntman.
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