It's been a hard day's semi-century. But the passage of 50 years since the debut of A Hard Day's Night hasn't robbed the Beatles' first and best movie of any of its youthful zest or Fab-ulosity. In honor of the anniversary of the July 6, 1964 opening night, here are some facts about the film and its wildly successful soundtrack you probably didn't know:

The famous weird chord that kicks off the album and film is… well, what is it? For five decades, guitar-strumming Beatlemaniacs have gone in search of the lost chord. The book All the Songs declared it was a D major 7th sus 4. In 2012, a mathematician made news by declaring that it involved a bit of trickery with George Harrison playing "a straightforward Fadd9 on his 12-string electric Rickenbacker guitar" but curling his thumb around the neck of the guitar to press down the bottom E string. But for many fans, the mystery was solved in 2011 when Randy Bachman (of Guess Who and BTO fame) filmed a lengthy explanation of how it was done, after being allowed to visit Abbey Road and listen to the master tapes. His conclusion was that it involved Harrison and John Lennon striking chords and Paul McCartney hitting a bass note simultaneously. But even that doesn't allow for the presence of a piano that some say is subliminally audible in the sacred chord.

The solo on "A Hard Day's Night" was a special effect that could not be reproduced onstage. For the instrumental break, music producer George Martin sat down at the piano and doubled Harrison's guitar part, which they played at half-tempo and an octave lower, before the inventive producer sped the tape up.

Legend has it that the lack of a love interest in the film was contractually mandated. Some source have claimed there was a clause in the movie's contracts ensuring the lads didn't woo any women, so as not to make any female fans insanely jealous. This may be apocryphal, although it does strike some viewers as odd that John Lennon sings "If I Fell" to Ringo Starr while young ladies are only allowed to look on.

The original lyrics of "If I Fell" revealed a seemingly crueler John. Originally, Lennon wrote, "I hope that she will cry/When she hears we are two," seemingly reflecting a growing disdain for his first wife, Cynthia. The line was eventually softened to eliminate any "hope" that the spurned woman in his life would end up in tears over discovering his new love.

The soundtrack was the only Beatles album ever to consist exclusively of Lennon-McCartney compositions. On previous records, the band had recorded cover material, and subsequently, Harrison and Starr would contribute as songwriters. "I'm Happy Just to Dance With You" marked the last time Lennon and McCartney would write a song for Harrison as a lead vocalist; Lennon suggested that the song was too formulaic for him to sing it himself.

"I'll Cry Instead" was written for the film but jettisoned by the director for lacking pep. The number was intended to be used for a scene where the Beatles escape from the back of a theater and run into a field, but director Richard Lester wanted something more joyful, so he substituted "Can't Buy Me Love," which had already been a hit before the movie's release.

Peter Sellers had a hit covering the title song. Sellers's Goons comedy troupe was a big influence on the movie's style of comedic filmmaking and the Beatles themselves. And the homage went both ways. In 1965, the actor had a top 20 hit in England by recording "A Hard Day's Night" in the style of… Lawrence Olivier playing Richard III.

Lester and Martin had "a nasty split" that ended their professional relationship. In his memoir, All You Need Is Ears, Martin writes of being "hardly on speaking terms" with Lester after a bad row during the scoring sessions. Martin recalled that Lester liked to play jazz piano and "he gave me the impression that he considered me inferior to him musically." One day when Martin was recording a cue for the instrumental score, Lester confronted him in front of the musicians about the "crap" and "absolute rubbish you'd written." Their antipathy ensured that Martin was not re-hired to do the score for Help!. Meanwhile, Martin expressed pride that he got an Oscar nomination for Best Adapted Score, while Lester went unrecognized by the Academy. Lester, in turn, griped that Martin actually only wrote about "45 seconds" of music for the movie.