The girls roll up is the chorus. Britney has the first verse to herself. Then her and Iggy shares the chorus. After the chorus there's a very catchy chant about pretty girls, then the beat gets lighter and less intense. Iggy does a short rap to begin the second verse. Then the beat comes back in and Britney starts singing. Then the chorus, then the chant, then Iggy does a longer rap than before to start out the bridge. Then Britney sings a few lines in the bridge. Chorus repeats twice, then the chant comes in, repeats twice, and the song ends suddenly.
According to a reliable source on PopJustice
