In the dense collapsing core of a star undergoing a supernova, electron-type neutrinos are produced by neutronization, and neutrino-antineutrino pairs of all types are produced by thermal processes. At some time the core plus an overlying mantle may become opaque to neutrinos, and large number densities of these particles may build up. Then scattering processes in which neutrinos can exchange energy are important for determing the energy distribution functions and the loss rates for the low-energy neutrinos which have smaller opacities. We calculate ..nu../sub e/-..nu../sub e/, ..nu../sub e/-nu-bar/sub e/, and ..nu../sub e/-..nu../sub mu/ scattering rates. We find that all three rates are comparable to that for ..nu../sub e/-e scattering and hence they also may play an important role. (AIP)