  In the standard supernova picture, type Ib/c and type II supernovae are
powered by the potential energy released in the collapse of the core of a
massive star. In studying supernovae, we primarily focus on the ejecta that
makes it beyond the potential well of the collapsed core. But, as we shall show
in this paper, in most supernova explosions, a tenth of a solar mass or more of
the ejecta is decelerated enough that it does not escape the potential well of
that compact object. This material falls back onto the proto-neutron star
within the first 10-15 seconds after the launch of the explosion, releasing
more than 1e52erg of additional potential energy. Most of this energy is
emitted in the form of neutrinos and we must understand this fallback neutrino
emission if we are to use neutrino observations to study the behavior of matter
at high densities. Here we present both a 1-dimensional study of fallback using
energy-injected, supernova explosions and a first study of neutrino emission
from fallback using a suite of 2-dimensional simulations.
