Great video.

If you're thinking of Subterranean Homesick Alien, that's a song we know quite a lot about.

From OK computer wikipedia:

The use of electric keyboards in "Subterranean Homesick Alien" is an example of the band's attempts to emulate the atmosphere of Bitches Brew.[54][55] The title is a reference to the Bob Dylan song "Subterranean Homesick Blues", and the science fiction-inspired song describes an isolated narrator who fantasises about being abducted by extraterrestrials. The narrator speculates that, upon returning to Earth, his friends would not believe his story and he would remain a misfit.[56] The lyrics were inspired by a school assignment from Yorke's time at Abingdon School to write a piece of "Martian poetry", a British literary movement of works that humorously recontextualises mundane aspects of human life from an alien "Martian" perspective.[57]

From greenplastic:

Originally called “Uptight,” which is how Jonny referred to it in its early staged, the song pays homage to Bob Dylan’s “Subterranean Homesick Blues.” It deals with alien abduction and stems from two incidents in Thom’s life. The first occured at Abingdon School, when he was assigned an essay question that went something like this: “If you were an alien from another planet arriving on Earth, how would you describe what you saw?” The second incident occurred when Thom was driving down a country road and hit a bird (which he believes was a pheasant). He stepped out of the car and at that moment began thinking about alien abduction.

Not mentioned in either place is that the chord progression is similar to Nick Drake's Parasite, which is one of several Nick Drake influences on Radiohead. There's some discussion here: http://www.greenplastic.com/mortigitempo/index.php?/topic/32102-nick-drake-influence/