The End of Time: Part Two - S4-E18
Audio problem: During the climax, when the Doctor has Wilf's old service revolver and is alternately pointing it at the Master and Rassilon, there's a cocking sound every time he turns. Not only is the handgun a revolver, so it only needs to be cocked once, the Doctor is only shown actually cocking the gun once, when he first points it at Rassilon. (00:44:10 - 00:45:55)
Continuity mistake: Before Martha uses Project Indigo, she doesn't have an ear piece. Then, after two quick shots of Daleks, when Martha says, "Bye, Jack," she does (and then takes it out). (00:17:56)
The Doctor: I'm not... I'm not... I'm not from Mars!
Rise of the Cybermen (1) - S2-E8
Trivia: Only eleven Cybermen costumes were built, but careful filming made it look as if there were more.
Last of the Time Lords (3) - S3-E13
Question: Why does The Master fear The Doctor forgiving him? What's he forgiving The Master for exactly?
Chosen answer: The Master knows that deep down, he deserves death for the crimes that he's committed throughout his life, and since he regards The Doctor as his arch-foe, he expects it to be at his hands. The fact that The Doctor is still willing to forgive him after everything the Master's put him through hurts him more deeply than death would.
Captain Defenestrator