Thread:Jacob.cinnamon/@comment-1632909-20150706010854/@comment-1632909-20150706022428

You're missing the fact that the sentence also says "that were seen in the film", which conflicts with the bit about the floor. If the sentence were "The dance between Rose and Greg features a similar glowing dance floor that was seen in the film...", it wouldn't make sense. It would need to be "to the one" or something like that, which is why the mdash is needed to separate the thoughts contained in the sentence.