  The characteristics of an extensive air shower derive from both the mass of
the primary ultra-high-energy cosmic ray that seeds its development and the
properties of the hadronic interactions that feed it. With its hybrid detector
design, the Pierre Auger Observatory measures both the longitudinal development
of showers in the atmosphere and the lateral distribution of particles arriving
at the ground, from which a number of parameters are calculated and compared
with predictions from current hadronic interaction models tuned to LHC data. At
present, a tension exists concerning the production of muons, in that the
measured abundance exceeds all predictions. This discrepancy, measured up to
center-of-mass energies of $\sim$ 140 TeV, is irresolvable through mass
composition arguments, constrained by measurements of the depth of the
electromagnetic-shower maximum. Here, we discuss a compilation of
hadronically-sensitive shower observables and their comparisons with model
predictions and conclude with a brief discussion of what measurements with the
new detectors of the AugerPrime upgrade will bring to the table.
