Alison Krauss made a surprise appearance during Ralph Stanley's performance Thursday night (July 31) at Nashville's Ryman Auditorium. To the surprise and delight of the crowd, she walked on stage early in Stanley's performance and joined him in singing "Angel Band." Krauss and Stanley worked together on the 2002 Down From the Mountain tour (a spinoff from the O Brother, Where Art Thou? film) and the 2004 Great High Mountain tour (inspired by the movie, Cold Mountain). In September, Krauss will rejoin Robert Plant for nine dates on the tour supporting their album, Raising Sand. Stanley was appearing with the Grascals as a part of the Ryman's annual bluegrass series.