A new interaction mechanism is described between neutrinos and dense plasmas. With the unification of the electromagnetic and weak forces, analogous processes should occur for intense neutrino fluxes as for photon fluxes. Intense EM waves excite parametric instabilities in nonlinear media and plasma in particular. Therefore, sufficiently intense neutrino fluxes should also cause similar parametric instabilities in dense plasmas. An important example is the production of Langmuir plasmons and lower energy neutrinos. In plasma physics, for electromagnetic waves, the process is known as stimulated Raman scattering and it greatly increases the interaction of the light with the plasma. We propose that the analogous process, for neutrinos, occurs in the plasma surrounding the core of a supernova due to the immense neutrino flux there and the fact that at some distance from the core the flux is strongly unidirectional. We develop a theory for stimulated scattering of neutrinos in plasmas based on the index of refraction for neutrinos which depends on electron density, conservation of energy and momentum for neutrinos plus plasmons and wave damping; we estimate approximate growth rates.