The longitudinal dynamical susceptibility of the Heisenberg ferromagnet is studied at short wavelengths and low temperatures. It is shown that identical results to order 1/S are obtained using (a) a spin decoupling technique, (b) a diagrammatic method using the Holstein-Primakoff transformation, and (c) a diagrammatic method using the Dyson-Maleev transformation. We thus conclude that there are no significant kinematic effects at low temperatures. Using the random-phase approximation, we find that the Dyson-Maleev interactions between magnons are too weak to support the existence of a zero-sound mode. Both these conclusions disagree with the recent results of other authors.