Mystery watch
A mystery watch is a generic term used in horology to describe watches whose working is not easily deducible, because it seems to have no movement at all, or the hands don't seem to be connected to any movement, etc.
One example is a type of mechanical watch where the movement is transmitted to the hands through a transparent crystal toothed wheel.
This first see-through watch, called in French montre mystérieuse (mystery watch), was invented by Hugues Rime and marketed by the French firm Armand Schwob et frère. As an item of historical/horological value, it is preserved in various museum collecions, such as British Museum, German Clock Museum, International Museum of Horology, Musée d'art et d'histoire of Neuchâtel and the National Watch and Clock Museum.