Revealing: When McDermott is being 'engulfed' by the black plastic chair, you can quite see him pulling it down on top of himself.

Revealing: In the UNIT tracking room, there is a flimsy railing behind the radar operators that Chinn knocks as Yates leads him off to the "direct" phone line, causing it to wobble badly. The Doctor then deals the railing another blow as he comes up to look at the console.

Audio problem: When Chinn tells the Brigadier of his agreement with the Axons, the movement of the actors around the set causes various loud wooden clumping sounds that are rather inappropriate for the organic interior of Axos.

Factual error: The Nuton power complex contains a cyclotron which, Winser explains, can accelerate atomic particles to the speed of light and beyond. There's even an instrument which measures the effect, with a scale marked in "x light". Unfortunately, relativity states that you can't accelerate particles to the speed of light (let alone beyond it), because at that point the particles would have infinite mass.

Revealing: The Filer vs. Filer fight in the lab is very amusing, not only because of the several glimpses of the stuntman doubling for Filer, but also because of the way the "metal" railings around the set wobble as they slam into them.

Continuity: As the Master escapes from Axos, he kills the UNIT soldier standing guard outside, whose beret falls off as he slumps to the ground. Cut to the Master standing over the corpse, and the missing beret instantly replaces itself on the head of the corpse.

Other: The Doctor gets Jo to do some mathematics to distract her. At one point she says "49 x 2=88", when it actually equals 98, then she says that "adding 10 equals 108". (In other words, Jo (Katy Manning) fluffed her line, got one figure wrong, then went back to script...).

Factual error: The calendar which shows the date to be Monday, 2nd March, 2472, is two days out. 2nd March 2472 will be a Saturday...and who made the calendar if the colonists left Earth over a year earlier?

Continuity: In part one, watch for the continuity error when Miss Hawthorne turns to face the policeman: her cape appears and disappears from around her shoulders from shot to shot.

Continuity: The hoofmarks seen by both Yeats and Benton from the helicopter appear to be huge when seen from the air. Yet, when the helicopter lands, the hoofmarks are suddenly much, much smaller.

Continuity: After completing the third summoning ritual, the Master turns towards the spot where Azal is about to appear. He has his arms lowered and Jo is stood to his left. In the next shot his arms are up, and Jo has moved to being in front of him.

Other: When the Master is in the cavern, he lights the candles with a taper, then shakes out the taper which snaps in half.

Revealing: When the Brigadier crosses over to the RAF and the plane, you can see the plane is a model with a stick to control it just under the nose.

Plot hole: It is never explained who - or what - killed the man in the churchyard during the first scene (early in part one). It cannot be Bok (the gargoyle) or Azal (the Daemon) as neither of them have awoken.