Circle of Life

"These human beings... consider their potential. From the day they arrived on the planet and blinking stepped into the sun... there is more to see than can ever be seen. More to do than-- no, sorry. That's The Lion King."

- The Doctor, to the Sycorax Leader

"Circle of Life" was a song from The Lion King that was quoted by the Doctor (with some alterations). (DW: The Christmas Invasion)

Behind the Scenes
Elton John sings the original version of the song. The song title does not get a mention on-screen. The original lyrics are slightly different, as the first line is, "From the day we arrive on the planet" (as opposed to the Doctor's version - "From the day they arrive on the planet".

This change, of course, makes sense, as the Doctor is speaking from his alien, Gallifreyan perspective. The line that the Doctor did not finish is, in the song lyrics, "More to do than can ever be done". John receives a further reference, and has a very brief cameo, in the later episode Love & Monsters.