  It was recently conjectured that the ratio of the shear viscosity to entropy
density, $ \eta/ s$, for any fluid always exceeds $\hbar/(4 \pi k_B)$. This
conjecture was motivated by quantum field theoretic results obtained via the
AdS/CFT correspondence and from empirical data with real fluids. A theoretical
counterexample to this bound can be constructed from a nonrelativistic gas by
increasing the number of species in the fluid while keeping the dynamics
essentially independent of the species type. The question of whether the
underlying structure of relativistic quantum field theory generically inhibits
the realization of such a system and thereby preserves the possibility of a
universal bound is considered here. Using rather conservative assumptions, it
is shown here that a metastable gas of heavy mesons in a particular controlled
regime of QCD provides a realization of the counterexample and is consistent
with a well-defined underlying relativistic quantum field theory. Thus, quantum
field theory appears to impose no lower bound on $\eta/s$, at least for
metastable fluids.
