The keys, of course! You watch them, knowing innately that something is not right. Then it hits you: the keys are not moving! You yank open the back of the Grand as you peer into the gloom. Not even in here, in the very heart of the machine, are the keys being played. What remains is an ethereal glow.
In the light of the tolling glow, a thing that seems to shimmer and move, you are able to identify a box. No; in fact, it is a music-player, one of those old-fashioned charmed pieces that make a sound when they are left open. And it is from this object that the sorrowful tune is being poured out.
Albeit a little hesitantly, you reach into the neon glow and lift out the music-box. Even in its own-generated light, you can tell that it is a thing of ornate beauty, small and heart-shaped, once pink but now faded, with a lost red symbol on its lid: an anti-clockwise swirl fading in to a dot.
You attempt to close the box with a snap, but, again, something is not quite right with the object. The light does not fully go off; the snap is louder than it should be. Thus, you discern that there is something hidden within the music-box.
You pry it open again, lifting the dainty object level with your eyes. There, you see a couple of things wedging the box open. You weave your fingers through to the foreign objects and pluck them out, surprised to see a set of keys that fall into your palm. Like the box they were kept in, these keys are ornately dainty, but in much less detail. However, they still retain the green-glow of the box itself. In fact, now the music-box matters little. Shutting it fully and cutting off the music, you rest it back on the lid of the piano, staring at your prize.
These are the real piano keys. But what are they for?