After the actors leave the stage, the audience go home and the crew clear the set, what evidence is there that a performance has ever taken place? A book exists after the reader has finished the story, and can be re-read at leisure, a CD remains as a testament of the music long after the band has argued and gone their separate ways, and a painting will stand the test of time, years, often centuries after the painter as gone to the big easel in the sky. But a theatre performance, by its very nature is a fleeting art form. A CD may be recorded of the cast of a musical, or a performance may be released on DVD, but once the curtain falls the actual performance has finished. You may read all the reviews you can find of the performance, ask each audience member to re-live what they saw on stage, but nothing can re-create the moment once it has passed. This is part of the magic of the theatre, its transience is very often what makes it so special.