Undertale - "The serene sound of a distant music box... It fills you with determination."

Y'know, the first time I came across the sealed room with the piano, the room of the statue and the room with the umbrella after that while doing the neutral run, I figured out the puzzle just by listening to the tune. Then, on my pacifist run, I realized that the arrows were materializing right there on the spot. I guess it must've been a product of a patch of something because, originally, they weren't there.