We provide a brief review of the contribution of thermally excited carriers to dispersion forces. In a metal, these carriers generate charge and current fluctuations whose spectral frequencies are comparable to $k_B T/\hbar$. They are very likely responsible for the "plasma vs. Drude" anomaly.
Comment: Proceedings of the 4th Symposium on the Casimir Effect, St. Petersburg, Russia, June 2019 (to be published)