I'd never seen a stage full of people suddenly beam from ear to ear on command, until...
...Mr. Z., my high school drama director, barked, "Smile!" at the actors during a rehearsal of The Music Man. Everyone's face brightened instantly. I started smiling, even though I was in the pit orchestra below the stage.
I still wonder why Mr. Z. chose that moment to decree smiles all around. After all, the cast was singing "Iowa Stubborn."