Doctor Who: 14 Cool Details In Steven Moffat & David Tennant's Silence In The Library Commentary
5. Catherine Tate Had Barely Any Time To Learn Her Lines For This Scene
As previously mentioned, the scene where Donna talks to the recently-munched-on Miss Evangelista came about because Moffat needed to make the episode longer.
It's a great moment for Donna and it's beautifully performed by Catherine Tate, which is all the more impressive when you learn that the actress had an extremely limited amount of time to practise her lines.
During this scene in the commentary, Moffat mentions that Tate "couldn't have had the script more than the night before", which seems to indicate that his various episode extensions were a last-minute thing.