  In the hot and dense medium of a supernova (SN) core, the nucleon spins
fluctuate so fast that the axial-vector neutrino opacity and the axion
emissivity are expected to be significantly modified. Axions with
$m_a\alt10^{-2}\,{\rm eV}$ are not excluded by SN~1987A. A substantial transfer
of energy in neutrino-nucleon ($\nu N$) collisions is enabled which may alter
the spectra of SN neutrinos relative to calculations where energy-conserving
$\nu N$ collisions had been assumed near the neutrinosphere.
