Vocalist Josh Franceschi told Virgin.com this is his favorite vocal on the album. He explained: "My favourite vocal on the album is in a song called 'Contagious Chemistry' where I think it's got enough aggression, 'cause it's quite an aggressive song, it's got enough aggression in my voice to really suggest that that's where it's coming from, and at the same time it's got like really nice delicate parts in it as well. So I'm really happy with that song, it's really good."
Will.I.am, literally dreamt up "I Gotta Feelin'." Said the Black Eyed Pea: "Have you ever had a dream where there's a melody in your dream? I'll wake up out of my sleep and record that! 'I Gotta Feelin' was one of those songs."