from http://en.wikipedia.org/wiki/Sheep_(song): During their tours in 1974, Pink Floyd played three new songs in the first half of the shows, followed by The Dark Side of the Moon in its entirety. Those three new songs were "You Gotta Be Crazy" (which would later become "Dogs"), "Shine On You Crazy Diamond" and "Raving and Drooling" (which would later become "Sheep").
During performances of "Raving and Drooling", a recording of a DJ at BBC Radio called Jimmy Young was played after being cut up and reassembled randomly. This was Roger Waters' idea of a man "raving and drooling" (or being insane). The lyrics of the song at this point were quite different from the ones that were to become "Sheep". "Raving and Drooling" was originally a more jam-based song, containing fewer lyrics.
Both "You Gotta Be Crazy" and "Raving and Drooling" were originally planned to be on the album following the tour (Wish You Were Here), but the plans were changed and they both ended up in different forms on Animals. In November 2011, versions of both tracks recorded at Wembley in 1974 were officially released as part of the Experience and Immersion versions of the Wish You Were Here album.
In live versions from 1977, backing guitarist Snowy White played bass guitar as Waters shared electric guitar duties with David Gilmour. The performance was almost identical to the album version except that it would give way to a slower ending with Richard Wright playing an organ solo.
Ian Peel, a musical columnist for The Guardian, noted the resemblance of "Sheep" to the Doctor Who theme, due to its bassline and sound effects.[2] Some critics have suggested that the song essentially reuses the bass part from "One of These Days", another track which had similarities to that same science fiction theme tune.