It is demonstrated that neither of the theories based on flaw size, surface flaw healing or residual stress adequately and consistently explain the strengthening and toughening phenomena in Alumina-SiC nanocomposites. SiC presence reduces the amount of amorphous (glassy) silica rich phase (SRP) in the nanocomposite relative to that found in monolithic Alumina and to a level that the effect of SRP is negligible. The reduction of SRP and the multipliable effect of microstructural features such as dislocations, crack/particle interactions and cleavage steps, observed in these materials at an extraordinarily small scale (due to the nano-size of the SiC particles), are suggested to be more consistent in explaining these phenomena. Owing to the nano-scale at which these features operate, which is far below the practical resolution limit of the Scanning Acoustic Microscope (SAM), it is also argued that the latter may not be a good method for studying these materials.