  Mixing above the proto-neutron star is believed to play an important role in
the supernova engine, and this mixing results in a supernova explosion with
asymmetries. Elements produced in the innermost ejecta, e.g., ${}^{56}$Ni and
${}^{44}$Ti, provide a clean probe of this engine. The production of
${}^{44}$Ti is particularly sensitive to the exact production pathway and, by
understanding the available pathways, we can use ${}^{44}$Ti to probe the
supernova engine. Using thermodynamic trajectories from a three-dimensional
supernova explosion model, we review the production of these elements and the
structures expected to form under the "convective-engine" paradigm behind
supernovae. We compare our results to recent X-ray and $\gamma$-ray
observations of the Cassiopeia A supernova remnant.
