Since this has no explanation and there are people like me who don’t follow the Simpsons but are huge Don Hertzfeldt fans, DON HERTZFELDT (maker of Rejected and a bunch of other great works of animation) made a couch gag for The Simpsons and it’s incredible (and should really be viewed in video form here).
This heart-shaped silver locket holds a blue, glass, heart-shaped inside which glows bright blue in the dark. The locket features ornate carving to accent the piece and to provide a unique and enchanting lighting effect. Hung on a silver-plated chain. Sold on Etsy.