Matthew Graham found writing for two Doctors easy, as The Eleventh Doctor had a constant "internal dialogue" and was always finishing his own sentences.
As the Doctor passes the wall of eyes, he says "The eyes have it", a reference to the announcement in the British House of Commons, where the words "The ayes (or the noes) have it" are uttered by the Speaker of the House after a vote.
It was originally planned that Jennifer would eat Buzzer, but The Mill decided only the shadows of the action would be shown on the wall. All of this was cut from the final episode, with the exception of Jennifer's elongated mouth as she advanced towards him.
The original script explained that Jennifer has a perfect memory, and so her Ganger was able to remember every terrible thing that had happened to the Flesh.