Neutrinos interact only weakly with ordinary matter. Yet in certain astrophysical contexts, such as supernova explosions, the coupled interactions between neutrinos and dense, highly ionized plasmas contribute significantly to a system's evolution. Modeling such systems is complicated enough even in the absence of neutrinos, and it normally requires analytic approximations or detailed numerical simulations. Adding neutrino effects entails further compromises; past approaches, for example, typically consider energy exchange between neutrinos and a neutral fluid. Now Fernando Haas and Kellen Alves Pascoal (Federal University of Rio Grande do Sul, Brazil) and Tito Mendonça (University of Lisbon, Portugal) propose a new framework for integrating relevant aspects of neutrino and plasma physics. Their approach, which they dub neutrino magnetohydrodynamics (NMHD), systematically extends MHD, which treats a plasma's electrons and ions as fluids and considers the dynamics of the magnetic field they produce, to include the weak interaction, which in particle physics describes the coupling between neutrinos and electrons. Adopting standard simplifying assumptions from MHD theory, the researchers obtain a set of 11 coupled partial differential equations that they show should hold over a range of astrophysical conditions. In particular, they find that neutrinos can prevent magnetic field lines from freezing, even in an ideal plasma. They also derive a new, neutrino-driven plasma instability that should play a central role in a supernova's strongly magnetized environment. (F. Haas, K. A. Pascoal, J. T. Mendonça, Phys. Plasmas 23, 012104, 2016.)