The World's Most Expensive Object by Weight

It doesn't take long for Tom Scott to unveil the most expensive object by weight, if that's what you are watching this for. And he tells us its history and the reasoning behind why it's so expensive. However, you might wonder how this thing was selected for that very specific title. It all goes into how you define each term. "Object" must be a non-fungible discrete unit. "Expensive" doesn't exactly mean value. You get the idea. I understand why defining every term one uses is so important, because any time I label something superlative in a simple manner, I hear from commenters about exceptions and stretches until, well, until I'm just wrong. An example is the post just before this one on the last public execution by guillotine. The word "public" is necessary since the French government continued to behead people long afterward. Tom is a lot better at explaining that than I am.