Minor key instead of major key which means different possible scale which can change the timbre (emotion) of the song. For example "Hey Jude" is in F major so the scale would be F G A Bb C D E , however this is now a minor key and the relative key for F major is D minor so now the notes become D E F G A Bb C. However scales in the minor key can be natural (same as major), harmonic (7th note is raised a 1/2 step to E# on the way up and on the way down) and melodic (6th and 7th note are raised a 1/2 step on the way up and lowered a 1/2 step on the way down where the scale becomes F G A Bb C D# E# on the way up and E natural D natural C Bb A G F on the way down. Changing 1 or 2 pitches from what you're expecting can have a huge effect on the song.