Continuity mistake: When Amy is being pulled into the ground, there's a shot of her arms where the Doctor's hand gripping her left arm is missing. (00:13:38)
Audio problem: After landing, the Doctor comes out and jumps in place several times. As he does, the sounds of his landings don't sync up with his motions. (00:04:55)
Continuity mistake: Throughout this episode, Amy's earrings seem to disappear and reappear.
Plot hole: When the Doctor realises that something is coming up from below ground, he tells Nasreen and Tony that at the speed the three transports are coming, the underground arrivals will reach the surface in 12 minutes. The rushed preparations that ensue, including hurrying from the drill hall to the old church and setting up a surveillance network outside, couldn't have taken less than 12 minutes to set up, especially given that they also had to: inform the others trapped inside the shield (Rory, Ambrose and Elliot), inform Rory and Ambrose that their significant others (Amy and Mo) were missing, run between the old church and the block of houses and gather supplies. And, lest we forget, there's also Rory and the Doctor arguing about what happened to Amy and Ambrose's initial skepticism as to what is occurring.
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