  Thermal pair annihilation of heavy particles, such as dark matter or its
co-annihilation partners, can be strongly influenced by attractive
interactions. We investigate the case that pair annihilation proceeds through a
velocity-suppressed $p$-wave operator, in the presence of an SU(3) gauge force.
Making use of a non-relativistic effective theory, the thermal average of the
pair-annihilation rate is estimated both through a resummed perturbative
computation and through lattice simulation, in the range $M/T \sim 10 ... 30$.
Bound states contribute to the annihilation process and enhancement factors of
up to $\sim 100$ can be found.
