  We consider the next-to-leading order thermal production rate of heavy
right-handed neutrinos in the non-relativistic regime m_top < pi*T << M, where
m_top refers to the electroweak scale. Rephrasing the problem in an OPE
language and making use of different techniques than a previous analysis by
Salvio et al, we confirm the general structure of their result and many of the
coefficients. We also extend the analysis to the next order in the
non-relativistic expansion, thereby revealing the leading non-trivial momentum
dependence, as well as to NNLO in couplings, revealing the leading sensitivity
to thermal resummations. Our results are expressed as a sum of simple "master"
structures, which renders them a suitable starting point for determining the
next-to-leading order rate also in the relativistic regime pi*T ~ M.
