Although she and Arthur often throw glamorous dinner parties, Miranda feels out of place and consistently uncomfortable in his community of actors and Hollywood luminaries. As Arthur jokes about the purpose of one of these parties, he uses an idiom to joke about what he and his wife are trying to achieve, foreshadowing their future troubles:
There are ten guests here tonight, an intimate evening to celebrate both the anniversary and the opening weekend figures. “Two birds with one stone,” Arthur said, but there’s something wrong with the evening, and Miranda is finding it increasingly difficult to hide her unease.
When a person uses the idiom “kill two birds with one stone,” they usually mean that they are attempting to solve two problems with a single overarching solution. However, Arthur refers to “killing” two celebrations, not two problems. It’s his wedding anniversary to Miranda, and his latest film has achieved an excellent opening weekend. Arthur’s use of the phrase suggests that getting this party over with would be a welcome outcome. However, in this context, it comes across as dismissive. By framing their anniversary as a “bird” to kill with a "stone," Arthur has reduced his marriage to one half of a minor problem.
Miranda’s discomfort reinforces this impression. She recognizes that something feels off and “wrong with the evening,” even if she doesn’t quite know what it is. Her growing unease here suggests that she knows something is amiss with her marriage. It subtly foreshadows their upcoming divorce, as well as providing context for Miranda’s discomfort with Arthur’s glamorous life as an actor.