Andy Ihnatko, at Andy's Ihnatko's Celestial Waste of Bandwidth. He writes about a topic I seldom care about, Opera, but makes me care about this story:

Kim, an elite professional, accelerates through every curve. She seems to have no limitations; every note she sings is a conscious choice and she’s in full control of her instrument throughout. And keep in mind that as impressive as this performance was, it was all in a day’s work for her. She would do it again and again and again throughout the show’s run. So. One night, Kim got sick and Rachele Gilmore was forced to make her Met stage debut on just three hours’ notice. You must read his article, and watch the two videos embedded within it.