Zoë Wanamaker was unable to attend the studio session in Cardiff and recorded her lines as Cassandra later in a sound studio in London. She was so impressed with the show when it went out that, when asked to return for New Earth (2006), she made sure she was available to attend the studio recording and recorded her lines live.
Bad Wolf Reference: The Moxx of Balhoon says "This is the Bad Wolf scenario" to the Face of Boe.
The majority of the series' effects budget were used up for this episode, because the story required more CGI effects than any other story. A sequence in which the viewing gallery tilted on its axis had to be dropped due to the expensive budget.
Russell T. Davies has said on many occasions that he was inspired to create Cassandra upon viewing skinny Hollywood actresses at the Academy Awards. On 2 April 2006, the Sunday Mirror quoted Davies: "It was horrific seeing those beautiful women reduced to sticks. Nicole Kidman struck me in particular. Nicole is one of the most beautiful women in the world. But she looks horrifying because she's so thin. It's like we're killing these women in public. We watch while you die."
When Jabe brings up the subject of the Last Great Time War, the Doctor is discretely seen shedding a single tear, in perhaps the only time the Ninth Doctor is shown to visibly cry on-screen.