Chelsea Zellner and Steve Newbrough
The quick answer is that Beyoncé uses a bass lines to imply the minor iv chord in the second chorus right on the word “shoulda...” (this is 51 seconds into the song). Notice how this makes you feel as a listener. What was light hearted jam suddenly becomes more serious and heavy.
The harmonic analysis of Single Ladies is actually hotly debated in the music theory community. This piece of music is extremely unique, and deceptively complex given the apparent simplicity of it on the page. It contains a pretty simple melodic line, percussive accompaniment, and very little harmonic support (pitched instruments playing harmonies). Because of this, there is some room for interpretation. While some minds feel this song is an example of polytonality and some pretty complex borrowed chords, there is abundant evidence pointing to the...