New this week Factual error: We know the episode takes place on 23 November, 1963 because the first episode of Doctor Who is about to come on TV when Ace leaves the room. JFK was assassinated less than 24 hours ago, and nobody seems to be affected. Granted, the military characters have other things on their minds, but none of the civilians wear black armbands or even mention that the biggest news story of the year that just happened.
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.
Revealing mistake: 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.
Other mistake: 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.