“Less than six hours before the curtain was to rise for the final performance of Pittsburgh Opera’s production of La traviata, the lead singer, Danielle Pastin, was sick, and it was unclear whether she would be able to perform. Was [Claudia] Rosenthal – the understudy who had been playing the small role of Annina – prepared to play Violetta instead? … Oh, and by the way, she would still have to sing Annina’s part, too.”