This reminds me of the eternal Episodes problem. The first part of the ballet is "abstract" dance to atonal music, and the audience invariably sits through it in baffled silence. They have no clue as to when it ends, so there has to be someone in the house who's a ballet veteran, and a fearless one, who is willing to clap decisively at the proper moment. Then the rest of the audience will follow.
Of course, the opposite problem also occurs. In Liebeslieder Waltzes, despite the fact that the program clearly states that the ballet is in two parts and that the curtain will be lowered between them, many members of the audiences applaud insistently after the first part, expecting the dancers to come out to bow. The last time I saw it, a woman in the fourth ring continued to clap loudly after everyone else had given up, so that I had to whisper to her, "Ma'am, they're not coming out. This is just a pause." She raised her eyebrows but stopped clapping.