Revealing Mistakes: The Cyber voices are dubbed in, which xometimes causes the opening and closing of their mouths to be inconsistent with the spoken lines.
Factual Error: When Mondas is first seen in detail, its continents are found to be identical to Earth's. The planet is rotating so that all of the continents can be seen. While making for a nice visual, this would mean that Mondas is spinning on its axis once every few seconds - tens of thousand of times faster than Earth. This would be such a fast rotation that the objects would be unable to stay on the surface or the planet would become extremely oblate or completely disrupted.
The Cybermen's helmets were held together with Sellotape, which can clearly be seen in this episode.
Krail: You must come and live with us.
Polly: But we cannot live with you! You're different. You've got no feelings.
Krail: Feelings? I do not understand that word.
The Doctor: Emotions. Love, pride, hate, fear. Have you no emotions, sir?
Krail: Come to Mondas and you will have no need of emotions. You will become like us.
Ben [ regarding the Cyberman ]: Just imagine trying to tackle one of those things with a screwdriver!
This story (Episodes 2 and 4) was the only time that Roy Skelton provided a Cyberman voice. These Cybermen speak in unnatural, mechanical tones, with unusual emphasis and pronunciation. In future stories, more naturalistic voices are provided by the actors in the suits.