  We present high-resolution of spectroscopy of four stars in two candidate
ultra-faint dwarf galaxies (UFDs) Grus I (Gru I) and Triangulum II (Tri II).
Neither object currently has a clearly determined velocity dispersion, placing
them in an ambiguous region of parameter space between dwarf galaxies and
globular clusters. No significant metallicity difference is found for the two
Gru I stars, but both stars are deficient in neutron-capture elements. We
verify previous results that Tri II displays significant spreads in metallicity
and [$\alpha$/Fe]. Neutron-capture elements are not detected in our Tri II
data, but we place upper limits at the lower envelope of Galactic halo stars,
consistent with previous very low detections. Stars with similarly low
neutron-capture element abundances are common in UFDs, but rare in other
environments. This signature of low neutron-capture element abundances traces
chemical enrichment in the least massive star-forming dark matter halos, and
further shows that the dominant sources of neutron-capture elements in
metal-poor stars are rare. In contrast, all known globular clusters have
similar ratios of neutron-capture elements to those of halo stars, suggesting
that globular clusters form as part of relatively massive galaxies rather than
in their own dark matter halos. The low neutron-capture element abundances may
be the strongest evidence that Gru I and Tri II are (or once were) galaxies
rather than globular clusters, and we expect future observations of these
systems to robustly find non-zero velocity dispersions or signs of tidal
disruption. However, the nucleosynthetic origin of this low neutron-capture
element floor remains unknown.
