Trivia: In "Human Nature", when John Smith (The Doctor's human identity) is talking about his parents, he says their names are Sydney and Verity. Sydney Newman was the creator of Doctor Who and Verity Lambert was the first producer. (00:30:00)
Trivia: Possible Spoiler: At the time of this writing, it is generally believed that the "Mister Saxon" referred to throughout Season 3 will turn out to be The Master. One piece of evidence backing this theory is The Master's penchant for anagrammatic aliases: Mister Saxon is an anagram of "Master No Six," and if it's true, John Simm would be the 6th actor to play The Master. [Russell T Davies (who wrote most of the episodes) has said that the anagram is pure coincidence which was picked up by some people, but was completely unintended. Still interesting regardless.]
Trivia: Bernard Cribbins, who plays Wilfred Mott, once appeared in a much earlier Doctor Who-related story - he played Tom Campbell in the feature film Dalek Invasion Earth 2050 AD, with Peter Cushing as the movie's alternate, human Doctor.
Trivia: At the end of the episode, Astrid is set loose to travel through space and time. Astrid is an anagram of TARDIS, which does the same thing.
The Sound of Drums (2) - S3-E12
Trivia: During the episode, the Master is seen watching the Teletubbies on his laptop. This is very similar to an episode during the John Pertwee era where the Master, played by Roger Delgado, is seen watching an episode of The Clangers whilst in prison.
The Sound of Drums (2) - S3-E12
Trivia: When the Doctor turns Martha's TV around to find the bomb, there's a sticker above it from Magpie Electricals, the TV shop from "The Idiot's Lantern." (00:14:25)
Trivia: When the Doctor sends the banknotes flying out into the street, all of the notes have David Tennant's or Phil Collinson's (the producer) faces on them, with quotes from the Fourth and Tenth Doctor (like "no second chances - I'm that sort of a man"). The notes have since become collector's items, selling often for about 50 pounds each.
Trivia: The controller used for the Christmas decorations is an old Nintendo 64 controller with parts added.
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.