Castrovalva:

10ep 1 – The Doctor's footwear regenerates with him! Watch as he changes from long brown leather boots in the pre-credits sequence to brown shoes in the episode proper.
[Apparently the boots actually belonged to Tom Baker and he simply took them with him when he finished filming the regeneration scene...!]

20ep 1 – And it's not only the Doctor's footwear that behaves strangely: Peter Davison's hair is light brown in the pre-credits regeneration sequence but changes to near-platinum blond in the rest of the episode.

30ep 1 – When Tegan drives the ambulance away from the Pharos project guards, there's a shot of her pulling the steering wheel sharply to the right, followed by Nyssa falling into the passenger seat. However, Tegan's manoeuvre would have flung Nyssa away from the passenger seat instead of towards it.

40ep 1 – When Nyssa closes the TARDIS doors, she says "This works the doors — that's all I know about these controls". She then immediately contradicts herself by moving around the console and turning the scanner on!

50ep 1 – When the Doctor is levitating in the Zero Room, the shot of him overlaid onto the main picture is reversed — see the question-mark symbol on his shirt lapel, and also the parting in his hair.
[You'll already have noticed this if you listen to the DVD commentary, where Peter Davison takes great pleasure pointing it out]

60ep 2 – Nearly 5 minutes into episode 2, while the Doctor is sitting in the wheelchair, look sharp for a whopping great boom shadow right across Peter Davison's jacket.

70ep 3-4 – The "crazy-quilt" broken-up view of Castrovalva from the Doctor's window only occurs in one shot (the Part 3 cliffhanger) — but there are several shots on either side of it which show only the normal view out the window.

80ep 4 – When Nyssa and Tegan bring the Zero cabinet back to the Doctor's room, Nyssa knocks on the door. If you watch carefully, you'll notice that the sound of her knocking starts before before her hand even touches the door.

90ep 4 – While Mergrave and Ruther are searching for the cause of the broken window, there's a scene when they look meaningfully at each other. Right before the camera cuts away, the picture wobbles noticeably.

100ep 4 – When the tapestry starts to fade and Adric appears, the shot of Adric is reversed — his red shirt pocket appears on his right-hand side instead of the usual left-hand side.

110ep 4 – In the final scene (as the travellers are jogging back to the TARDIS), a fence is visible on the supposedly deserted planet.

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