Bang Bang (as you know) is sung by Jessie J, Ariana Grande and Nicki Minaj. Did you know in 2 unlraked versions Dove Cameron or Demi Lovato replaced Ariana Grande?
Once in a concert, Demi Lovato sang Ariana Grande's part. She afterwards revealed she was going to be featured in Bang Bang but Ariana Grande asked first. But she figured she owed it to her fans and performed it live.
Dove Cameron was also a candidate for the 2nd Voice in Bang Bang, but didn't make the cut because her voice was off. She then tried Side to Side with Ariana Grande and Nicki Minaj. Although their schedules didn't match. Luckily, they did sing a song together on Hairspray.