Audio problem: In episode 3, when the dog is barking at Sam's house and is abruptly silenced (apparently by an Auton), the sound is obviously not a dog barking. It sounds a bit like a man pretending to be a dog, and going "woof woof" not very convincingly.

Audio problem: The music accompanying the closing credits fades down part way through (at a different point in each of the four episodes) and simultaneously fades up at a different point, the net result being a rather disjointed-sounding edit.

Revealing: When the Doctor falls out of the TARDIS, near the beginning, he nearly manages to pull off the entire TARDIS door.

Audio problem: When the Doctor arrives at UNIT HQ in his stolen car, he speaks to a guard. We see close ups of the guard twice...but watch the brief clip of The Doctor (Jon Pertwee) between the two and you can just see that his lips aren't moving even remotely in synch with the words. (In fact, it is just a repeat of the previous shot of The Doctor, with new lines dubbed in).

Plot hole: The Brigadier met the Doctor previously in 'The Web of Fear' and 'The Invasion', both Second Doctor (Patrick Troughton) stories. In 'The Web of Fear', the TARDIS was trapped in the tunnels, not to be seen until the end of the story...and in 'The Invasion' the TARDIS was invisible. So how does the Brigdier know that the Police Box is anything but an emergency phone booth?