We’ve all seen singers go wrong. Forgetting words, missing entries, skipping verses – it happens often enough, and is generally cause for little more than some awkward laughter and a second attempt. Never, however, have I seen a wrong entry (as ill-luck would decree, in the only sacred work of the programme) greeted with a resonant expostulation of “Oh, shit” from the performer, followed by minor audience uproar and many apologies. It wasn’t the finest moment of the evening for Juan Diego Flórez, but – loath though I am to admit it – it wasn’t the worst either.