When The Doctor and The Master are speaking to each other the phone, they really are talking to the other person. Instead of having the lines read to them on the set, David Tennant and John Simm called each other in order to make the scene more authentic.
As the Toclafane remove one tenth of the population Noel Clarke's (Mickey Smith) voice can be heard during the alarm calls.
Martha's suggestion that the Doctor and the Master are brothers (dismissed by the Doctor) was Russell T. Davies' response to a popular fan theory he found rather daft.
The television in Martha's flat was made by Magpie Electricals, the same television-maker featured in The Idiot's Lantern (2006).
Before introducing the Toclafane, The Master offers his wife a Jelly Baby, which was the candy of choice for Fourth Doctor Tom Baker.