A Dalek is added to the model that is used during the reprise, thus giving the impression that a Dalek has appeared out of nowhere during the opening scene.
The Doctor says that if the Earth is moved, it will upset the entire constellation. This statement has no meaning. A constellation is nothing more than a grouping of stars according to a man-made picture. The stars in the constellation are not necessarily related in any scientific way.
When the Doctor, Susan, David and Tyler are looking over the cliff, the Doctor leans against a rock, the wobbling of which reveals it to be made of polystyrene.
During a scene in the Dalek control room, the pedal mechanism that allows the actor to control the movement of the Dalek Supreme can be heard creaking. The Daleks supposedly use static electricity to glide along the floor.
During the rebellion in the Dalek mine, which is located in Berkshire, the Kew Bridge set can be seen through an open doorway, revealing that the sets were side-by-side on the studio floor.
While Barbara distracts the Daleks with tales of historical events, Jenny is sabotaging the Dalek's control room equipment but is clearly miming the sabotage.
When Barbara and Jenny's plan fails, the Daleks restrain them and attach them to a pillar by neck braces. Fortunately, having been attacked by two people, the Daleks have exactly two neck braces. And fortunately, one is placed at the correct height for a tall woman (like Barbara), and one is placed at a lower height, suitable for a shorter woman (like Jenny).
While the Doctor and Tyler are pressed up against the wall hiding, each Dalek exits the room one at a time. The last Dalek's viewer passes by the Doctor looking directly at him but doesn't stop to capture him.
William Hartnell flubs the lines "if they succeed it will upset the entire constellation. We've got to prevent it."
William Hartnell flubs the line, "we might be able to immobilize the Daleks."