Other mistake: When the Doctor gets George's psychic cry for help, he's shown reading the message without opening the wallet containing the psychic paper. This despite the fact that all previous instances of the Doctor receiving psychic messages this way has required him to open the wallet, suggesting that the wallet itself does not display the message. (00:02:02)
Continuity mistake: When Amy and Rory are searching the darkened kitchen, the flashlight Rory holds switches hands between cuts when it starts turning on and off. (00:13:52)
Continuity mistake: When Purcell is sinking into his carpet, just after a shot where he's shown having sunk into the floor up to his waist, we see a shot focusing on his dog where Purcell's legs are visible as he falls forward onto his hands, despite his legs having already been pulled under. (00:23:38)
Continuity mistake: When Alex is hugging George after rescuing him from the peg dolls, George's arms are down in shots facing Alex, but his left arm is up in shots facing him. (00:37:23)
Revealing mistake: When the landlord, Purcell, wakes up on his floor because his pet dog is licking his hand, we see a few pieces of dog food fall from his fingers - should have been a re-shoot, but all credit to the actor, he knows it has happened and is quick to hide them again. (00:38:38)
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