In terms of chords and melody, The Zombies Ate Your Brains is more complex than the typical song, having above average scores in Chord Complexity, Melodic Complexity, Chord Progression Novelty and Chord-Bass Melody.
The Zombies Ate Your Brains is written in the key of A Locrian. According to the Theorytab database, it is the 5th most popular key among Locrian keys and the 77th most popular among all keys. The A Locrian scale is similar to the A Minor scale except that both the 2nd and the 5th notes (B♭ and E♭) are a half step lower. This means that the characteristic "home base" chord of A Locrian has a dissonant diminished quality (a˚), which makes it a very uncommon choice for songs. See the A Locrian Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!