
Continuity mistake: When Nick is singing "Spend This Night with Me", he brings up a girl from the audience. Watch the background. When it shows another girl from the audience, in the next shot, you can see a speaker that wasn't there before. Moreover, when he picks the girl, we can see that there isn't anyone at her left side. But a few seconds earlier she was sitting between two girls (the one at her left was wearing a white shirt). (00:42:05)
Chosen answer: The actors were weighted down with lead plates. Oxygen tanks were kept just out of picture, and the actors used them to breathe between takes. The takes were short enough to allow the actors to hold their breath through them. The short takes were then cut together to appear as one long fight. Sound effects were added post-production.