 It would seem, then, that curvature pathology as characterized based on the behavior of tidal forces is not in any physical sense a well-defined property of a region of spacetime simpliciter. When we consider the physical manifestations of the curvature of spacetime, the motion of the device that we use to probe a region (as well as the nature of the device) becomes crucially important for the question of whether pathological behavior manifests itself. This fact raises questions about the nature of quantitative measures of properties of entities in general relativity, and what ought to count as observable, in the sense of reflecting the underlying physical structure of spacetime. Because apparently pathological phenomena may occur or not depending on the types of measurements one is performing, it seems that purely geometrical pathology does not necessarily reflect anything about the state of spacetime itself, or at least not in any localizable way. What then does it reflect, if anything? Much work remains to be done by both physicists and by philosophers in this area, i.e., the determination of the nature of physical quantities in general relativity and what ought to count as an observable with intrinsic physical significance. See Bertotti (1962), Bergmann (1977), Rovelli (1991, 2001 in  Other Internet Resources, henceforth OIR,  2002), Curiel (1999) and Manchak (2009a) for discussion of many different topics in this area, approached from several different perspectives. 