Hoggy Warty Hogwarts

The Hogwarts school song, was, at times, performed by students at Hogwarts School of Witchcraft and Wizardry before the beginning of the first term of a new school year. Fred and George Weasley were known to sing it to "a slow funeral march" in 1991.

Lyrics
''Hogwarts, Hogwarts, Hoggy Warty Hogwarts,  Teach us something please,  Whether we be old and bald,  Or young with scabby knees,  Our heads could do with filling,  With some interesting stuff,  For now they're bare and full of air,  Dead flies and bits of fluff,  So teach us things worth knowing,  Bring back what we've forgot,  Just do your best, we'll do the rest,  And learn until our brains all rot.''

Behind the scenes

 * The song's first appearance was in Harry Potter and The Philosopher's Stone book but was never in the movie.
 * In The Harry Potter and The Philosopher's Stone book, the song didn't have a specific tune. Dumbledore said "Everyone pick their favorite tune."
 * In film version of Harry Potter and the Goblet of Fire, after Rubeus Hagrid says Harry Potter is soon to be "the youngest Triwizard champion there's ever been!", he, Ron Weasley, and Hermione sing the Hogwarts theme, just before Harry sees Barty Crouch Sr.'s dead body. The song is also featured in an earlier deleted scene where the students of Hogwarts sing it in order to welcome their guest from Beauxbatons Academy of Magic and Durmstrang Institute. As depicted in the deleted scene, Harry, Hermione and, bizarrely, Vincent Crabbe appear to enjoy singing it, while the Beauxbatons and Durmstrang students appear uncomfortable.
 * Dumbledore conjured an animated ribbon from the tip of his wand to form the lyrics, like a wizarding equivalent of a karaoke machine.
 * Dumbledore called for the school song when he was "feeling particularly buoyant." Its absence at the Welcoming Feast in later years was due to the times becoming darker.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Goblet of Fire (film)

Notes and references
http://www.youtube.com/watch?v=cn0AQ6h1xN0&feature=autoplay&list=PL8F3727D76D7E6390&lf=results_main&playnext=1

Hymne de Poudlard