As we waited for curtain-up on Scottish Opera’s new production of Bartok’s Bluebeard’s Castle a member of staff walked out on stage. Don’t worry, he reassured us, he wasn’t about to announce that a member of the cast was indisposed. Nervous laughter from the auditorium. Still in the same matter-of-fact tone, he carried on, and I’ll admit that only at this point did I twig that this wasn’t a member of staff and that he was actually delivering a cleverly skewed version of the librettist Bela Balazs’s spoken prologue to the opera — something more often omitted than performed.