  Perfect fluids are modeled by using an effective field theory approach which
naturally gives a self-consistent and unambiguous description of the intrinsic
non-adiabatic contribution to pressure variations. We study the impact of
intrinsic entropy perturbation on the superhorizon dynamics of the curvature
perturbation ${\cal R}$ in the dark sector. The dark sector, made of dark
matter and dark energy is described as a single perfect fluid. The
non-perturbative vorticity's dynamics and the Weinberg theorem violation for
perfect fluids are also studied.
