 Endurantists don’t think there is any four-dimensional object to do this explaining job. There are only the three-dimensional slices, which are just the single, persisting three-dimensional object (each slice is that object, at a different time). STR tells us that the persisting thing has different three-dimensional shapes with respect to different reference frames. The different shapes in different reference frames are correlated, but according to the endurance theorist there is no ‘underlying’ four-dimensional object to explain these correlations. Endurantists may respond by questioning the need for explanation here.