  We explain a method for computing the bulk viscosity of strongly coupled
thermal plasmas dual to supergravity backgrounds supported by one scalar field.
Whereas earlier investigations required the computation of the leading
dissipative term in the dispersion relation for sound waves, our method
requires only the leading frequency dependence of an appropriate Green's
function in the low-frequency limit. With a scalar potential chosen to mimic
the equation of state of QCD, we observe a slight violation of the lower bound
on the ratio of the bulk and shear viscosities conjectured in arXiv:0708.3459.
