Revealing Mistake: When Jo is helping Bert around a corner, she knocks a support strut out of position.
Continuity: When Jo sits up in the cable car, her helmet doesn't have a lamp. Switch to the medium shot and it suddenly does.
Stevens: Shall I terminate him? (in reference to the Doctor)
Guard: Well, well, well. Bit old to play games, ain't we?
The Doctor: I'm quite spry for my age, actually.
The Doctor: I've been wanting to meet you for a long time. Your paper on DNA synthesis was quite remarkable for your age.
Professor Jones: A promising youngster, huh?
The Doctor: No, no, no. I mean for the age that you live in.
The Doctor: Venusian aikido, gentlemen. I do hope I haven't hurt you!
The title sequence film over which the closing credits were superimposed for this episode (and Episodes Five and Six) was played backwards and upside-down, a result of the film being played backwards through the projector in order to save time during recording.