10 Doctor Who Details You Definitely Missed The First Time
9. Shifting TARDIS Shapes (Twice Upon A Time)
The 2017 Christmas special Twice Upon a Time is known for many reasons.
It was Peter Capaldi's final regular appearance as the Twelfth Doctor, it was David Bradley's first full appearance as the First Doctor, and it was Mark Gatiss' first appearance as a piece of fan service to himself.
With all this history flying around, it was easy to miss this tiny little reference to another monumental episode of Doctor Who.
While the two Doctors are chatting inside Number One's TARDIS, an inconsistency in the design of the walls can be spotted: the pattern changes from the traditional round things, to a hexagonal arrangement. And hang on a second, haven't we seen those hexagon shapes before?
Well... yes!
When Tom Baker's Curator approaches the Eleventh Doctor in 50th anniversary special The Day of the Doctor, he's standing in front of a wall of hexagons very similar to this one. And that's because it is this one.
Crew member Matt Sanders revealed that this was due to one of the old walls not being suitable for modern broadcast.
To get around this, the production team decided to just replace it with the hexagon moulds from The Day of the Doctor, and call it an easter egg.
Sneaky, but effective.