  In this paper, we explore the interior dynamics of neutral and charged black
holes. Scalar collapses in flat, Schwarzschild, and Reissner-Nordstrom
geometries are simulated. We examine the dynamics in the vicinities of the
central singularity of a Schwarzschild black hole and of the inner horizon of a
Reissner-Nordstrom black hole. In simulating scalar collapses in Schwarzschild
and Reissner-Nordstrom geometries, Kruskal and Kruskal-like coordinates are
used, respectively, with the presence of a scalar field being taken into
account. It is found that, besides near the inner horizons of
Reissner-Nordstrom and Kerr black holes, mass inflation also takes place near
the central singularity in neutral scalar collapse. Approximate analytic
expressions for different types of mass inflation are partially obtained via a
close interplay between numerical and analytical approaches and an examination
of the connections between Schwarzschild black holes, Reissner-Nordstrom black
holes, neutral collapse, and charge scattering. We argue that the mass
inflations near the central singularity and the inner horizon are related to
the localness of the dynamics in strong gravity regions. This is in accord with
the Belinskii, Khalatnikov, and Lifshitz conjecture.
