  A recent calculation shows that the observed energy density in the Unruh
state at the future event horizon as seen by a freely falling observer is
finite if the observer is released from rest at any positive distance outside
the horizon; however, it is getting larger and larger so that it is negatively
divergent at the horizon in the limit that the observer starts falling from
rest at the horizon, which corresponds to the infinite boost with respect to
the freely falling observer at a finite distance from the horizon. In order to
resolve some conflicts between the recent calculation and the conventional ones
in the well-known literatures, the calculation of the free-fall energy density
is revisited and some differences are pointed out.
