The big sectional contrast that happens in that song happens in the bridge on the words “someday I wish upon a star…”
I think there are two main things contributing to the contrast happening between the verse and the bridge. The big one is note length. The verse notes (on the words “somewhere over the rainbow”) are long and drawn out. There are a lot of whole notes and half notes sung in the verses, while the bridge is much quicker. A lot of the bridge is eighth notes whipping back and forth in contrast to the drawn out notes of the verses.
A second contributor to the contrast between the two sections of this song is the vocal range used within in each section. Right off the bat, the first two notes sung in the song jump up a whole octave. She sings “Some-“ and then “-where” jumps up an entire octave. So the instant we hear her vocals in the beginning of the song, we know there’s some range to the verse. It happens within the first two notes. This sets the standard for the verse to have a lot of range in it.
But then when Garland sings the bridge, most of the notes in “someday I’ll wish upon a star…” are very close together in pitch. Most of them are only two or three half steps from each other. The notes in that section are tight, from a pitch standpoint, based on the standard set in the previous verse. It’s a stark contrast from the wide ranging vocals of the verses.
With this song being so old, it's cool to see that this concept of contratsing sections is not going anywhere any time soon.
