It's not what we think it is. It's a dummy. Whether we're talking about a surface such as stone, metal or glass. Or things from nature: a tree, a leaf, a water droplet, a piece of fruit, or simply tracks in the sand. Or a whole room, or a sculpture. Not an obvious fake; nothing about it is wrong - it's more that everything looks too real. Making dummies, or being able to allow the borders between artificiality and reality to disappear. That is an art in itself.