At nonzero temperature, pions propagate through a thermal medium at less than
the speed of light. About low temperature, this effect begins not at ∼T2, but at next to leading order, ∼T4. We also derive the
generalization of the relation of Gell-Mann, Oakes, and Renner to nonzero
temperature.Comment: 11 pages, latex + sprocl.sty, talk given at Continuous Advances in
QCD'96, Minneapoli