Plot hole: The Doctor and Romana comment on a recording which has finished playing BEFORE they have entered the room. Not only that, but all the other characters behave as if The Doctor and Romana had seen this recording.

Revealing: In episode 1,watch out for the wires pulling K-9 along the beach. (Unlike a real dog, K-9 didn't take well to the soft sandy surface and sank into the sand. Pulling K-9 along on wires provided an illusion of movement when the motor inside wasn't up to the job...).