  In Denicol et al., Phys. Rev. D 85, 114047 (2012), the equations of motion of
relativistic dissipative fluid dynamics were derived from the relativistic
Boltzmann equation. These equations contain a multitude of terms of second
order in Knudsen number, in inverse Reynolds number, or their product. Terms of
second order in Knudsen number give rise to non-hyperbolic (and thus acausal)
behavior and must be neglected in (numerical) solutions of relativistic
dissipative fluid dynamics. The coefficients of the terms which are of the
order of the product of Knudsen and inverse Reynolds numbers have been
explicitly computed in the above reference, in the limit of a massless
Boltzmann gas. Terms of second order in inverse Reynolds number arise from the
collision term in the Boltzmann equation, upon expansion to second order in
deviations from the single-particle distribution function in local
thermodynamical equilibrium. In this work, we compute these second-order terms
for a massless Boltzmann gas with constant scattering cross section.
Consequently, we assess their relative importance in comparison to the terms
which are of the order of the product of Knudsen and inverse Reynolds numbers.
