BY JOEL LOBENTHAL [NY Sun, 27 December 2006]

Two incidents of raucously censorious opera audiences seem to have caught the public unaware in recent weeks. At the Metropolitan Opera, Placido Domingo was booed when he conducted a "La Bohème," in which Anna Netrebko sang her only Mimi of the Met season. Five days later at La Scala in Milan, Italy, Roberto Alagna, singing Radamès in Franco Zeffirelli's new production of "Aida," was greeted with catcalls at the end of his "Celeste Aida," early in Act I. Mr. Alagna beat a hasty retreat, and Antonello Palombi was thrown onstage to pinch hit.