[wildrhythms]

I'm still a little confused what the "harmonic surprise" is... is it a genre shift within a piece of music? Is it related to chord progression? Is it a key change?

The example in the article seems to hint at "harmonic surprise" referring to a simple genre shift:

>With its stark, sudden shifts between choral melodies in major chords and menacing percussive elements drawn from the trap subgenre, the song constantly defies the listener's expectations throughout. That's why "This is America" also tops the list of pop songs rich in so-called "harmonic surprise," or points when the music deviates from listener expectations.