  With the most trans-iron elements detected of any star outside the Solar
System, HD 222925 represents the most complete chemical inventory among
r-process-enhanced, metal-poor stars. While the abundance pattern of the
heaviest elements identified in HD 222925 agrees with the scaled Solar
r-process residuals, as is characteristic of its r-process-enhanced
classification, the newly measured lighter r-process elements display marked
differences from their Solar counterparts. In this work, we explore which
single astrophysical site (if any) produced the entire range of elements
($34\leq Z\leq 90$) present in HD 222925. We find that the abundance pattern of
lighter r-process elements newly identified in HD 222925 presents a challenge
for our existing nucleosynthesis models to reproduce. The most likely
astrophysical explanation for the elemental pattern of HD 222925 is that its
light r-process elements were created in rapidly expanding ejecta (e.g., from
shocked, dynamical ejecta of compact object merger binaries). However, we find
that the light r-process-element pattern can also be successfully reproduced by
employing different nuclear mass models, indicating a need for a fresh
investigation of nuclear input data for elements with $46\lesssim Z\lesssim 52$
by experimental methods. Either way, the new elemental abundance pattern of HD
222925 -- particularly the abundances obtained from space-based, ultraviolet
(UV) data -- call for a deeper understanding of both astrophysical r-process
sites and nuclear data. Similar UV observations of additional
r-process-enhanced stars will be required to determine whether the elemental
abundance pattern of HD 222925 is indeed a canonical template for the r-process
at low metallicity.
