"It was a simple request, but one that could freeze the notes in a singer's throat. A renowned conductor had chosen the young mezzo-soprano Vivica Genaux to record an album of showy Baroque arias - her first solo recording. In preparation, Genaux was singing through the music with the conductor. She finished an aria.

'That was very nice," he said. "But now do it with a real trill.'

from "Reaching musical heights: the trill of it all"