In the London production, if I recall, there is an overture, (yes, a Grease overture), followed by Sandy and Danny on opposite sides of the stage, on balconies singing a wistful, abbreviated version of "Sandy." As the song ends abruptly, the orchestra comes to life, blares the opening chords of "Grease is the Word," the brick wall splits, smoke pours out and the Pink Ladies and Burger Palace Boys are standing there ready to sing.
"Y'all have a GRAND day now"