When a system at finite temperature is perturbed, the perturbation eventually thermalizes, and the correlation functions decay to zero.  However, the precise functional behavior of the correlators is an open problem. In this talk, I will explore a class of large N systems where the two-point function takes a remarkably simple form. In these models, the late-time decay is characterized by a discrete set of frequencies, reminiscent of the quasi-normal modes of a black hole. After explaining the classical intuition behind these frequencies, I will work out the case of the SYK model in detail. Finally, I will comment on lessons for more general systems, including matrix quantum mechanics.