When Robert and Giselle are dancing together, and becoming more and more obviously infatuated with each other, there's a cut to a shot of Edward and Nancy dancing, and looking over their shoulders, one after the other, with obvious concern. I'm pretty sure that they must have had a brief conversation along the lines of "We'd better put a stop to this right now!" Perhaps some creative author could describe the dance from Edward and/or Nancy's perspective, and reconstruct the conversation between them that led Nancy to "cut in" before the "King and Queen's Waltz" was over. That might be the basis for a "Missing Moment" fanfic, that is, a scene that we know must have occurred in canon, but wasn't described in specific detail. If any creative writer wants to attempt this challenge, please drop me a line, and we can discuss it further.