The Vampires of Venice - S5-E6
Revealing mistake: When the Doctor begins climbing a pillar on top of the bell tower, we can see white sky on the central arch. Two other arches in the very same shot show really dark CG sky. (00:42:17)
The Vampires of Venice - S5-E6
Audio problem: When Francesco says "Did you just say something about Mummy?", his lips hardly move because of the fang prosthetic in his mouth, revealing that the line was dubbed back in afterwards. (00:39:00)
The Vampires of Venice - S5-E6
Factual error: Isabella is a black girl living in 1580 Venice. So how is it that she has perfectly straight hair, when modern hair care products won't be invented for centuries?
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