  In recent work we showed that, for a class of conformal field theories (CFT)
with Gauss-Bonnet gravity dual, the shear viscosity to entropy density ratio,
$\eta/s$, could violate the conjectured Kovtun-Starinets-Son viscosity bound,
$\eta/s\geq1/4\pi$. In this paper we argue, in the context of the same model,
that tuning $\eta/s$ below $(16/25)(1/4\pi)$ induces microcausality violation
in the CFT, rendering the theory inconsistent. This is a concrete example in
which inconsistency of a theory and a lower bound on viscosity are correlated,
supporting the idea of a possible universal lower bound on $\eta/s$ for all
consistent theories.
