Revealing: In episode six, Ian helps Barbara get a grip on the rock and piece of the polystyrene pops off in his hand.

Revealing: Susan is supposed to be running through a forest. It is painfully obvious that, in fact, she is simply running on the spot against a back-projected film, and the branches that hit her are simply studio stagehands, hiding just out of shot, hitting the actress with twigs.

Revealing: In a few UNIT stories you can see where BBC TV badges have been on the UNIT land rovers

Revealing: You can see the studio floor in the "white void" outside the TARDIS door in early shots during episode one of this story.

Continuity: At the end of episode two, when the sink is emptied, the plug is placed on the bench. In the reprise for episode three, the plug is put back in the sink (thus enabling the miniaturized travellers to escape).

Continuity: The caption slide at the end of episode two reads: 'Next Episode: The Cave of Five Hundred Eyes'. While the title slide comes up at the start of episode 3, it simply says "Five Hundred Eyes".

Other: In episode seven, Kublai Khan refers to backgammon as a game of cards....obviously he's not an experienced backgammon player.

Revealing: In episode one, the Voord that falls down the pyramid shaft is very obviously a cardboard cutout.

Revealing: There are numerous scenes where the background Daleks are blown-up photographs. The most obvious is in episode five when the Daleks are discussing the radiation drugs.

Factual error: The story is set in 1289, when Marco Polo was anxious to leave China against Kublai Khan's wishes, so what's Polo doing on the Pamir Plateau?

Factual error: "Peking" is mentioned several times in this story, but this is an anachronism - this story is set in the year 1289 when Peking (now called Beijing) was known as "Khan-balik".

Plot hole: Yartek tried to disguise himself as Arbitan, by wearing Aribtan's robes, and pulling the hood over his giant rubber head. Strangely enough, no-one seems to notice that "Arbitan" is now suddenly speaking with completely different voice, and now has a two-foot-tall-head.

Continuity: In episode one, Barbara activates her travel dial only seconds before the others. But in episode two, she's been at Morphoton for quite some time - long enough to change clothes, pick fabrics and get food.

Visible crew/equipment: In episode one, when Ian is first seen inside the pyramid, someone stumbles through the background. Some have claimed this is Barbara, but it happens too fast to tell.

Visible crew/equipment: In episode one, when the Doctor is near the pyramid, someone's leg can be seen just before the shot ends.

Other: William has a bit of a nightmare, completely throwing the others during one scene by saying the same line ("It's not very likely") twice, and fumbling the line "You knocked both Susan and I unconscious". He also omits the scripted explanation for the melted clocks.

Plot hole: At the climax of episode 2, the Doctor is about to catch Lupton when the latter simply teleports to safety. So why didn't he do that in first place - before engaging in a 15-minute chase.

Plot hole: The Brigadier says UNIT HQ is 'a Top Secret establishment'. It is, in fact so secret that it has a large sign outside informing the world not only of its function, but also the name of the commanding officer...

Visible crew/equipment: The boom mic makes an quick appearance about 18 minutes into episode one. It is in the upper left corner when the camera switches from a close up of the Doctor and Susan to a medium shot of all four characters.

Other: In episode one, when the crew wonders what the Sensorites will do them, the camera zooms in on the Doctor as he says, "or kill us?". It then jerks with an audible click as though hitting something.