On 22 December 1895, Wilhelm Röntgen asked his wife to hold her hand over a photographic plate for a quarter of an hour. Anna Bertha Ludwig looked at the developed image of her own skeleton, wedding ring and all, and is said to have answered: I have seen my death.
A self-winding movement conceals its own mechanism. The oscillating weight is cut from a heavy alloy, often tungsten, so on a plate it burns brightest of anything in frame and swallows the gear train behind it. The leather strap, being only skin, barely registers at all.
The animal lives in the last and largest chamber and seals the rest behind curved walls. Every wall is pierced exactly once, by a tube called the siphuncle, which shifts gas and fluid between the chambers to trim the shell’s buoyancy. None of it shows from outside.
Security scanners fire two energies at once and colour what comes back: organic matter warm, metals cool, anything too dense to read through in black. The brightest object in most cabin bags is not the laptop or the camera — it is the pair of steel tubes inside the telescoping handle.