  The magnon dispersion of ferromagnetic SrRuO$_3$ was studied by inelastic
neutron scattering experiments on single crystals as function of temperature.
Even at low temperature the magnon modes exhibit substantial broadening
pointing to strong interaction with charge carriers. We find an anomalous
temperature dependence of both the magnon gap and the magnon stiffness, which
soften upon cooling in the ferromagnetic phase. Both effects trace the
temperature dependence of the anomalous Hall effect. We argue that these
results show that Weyl points and the anomalous Hall effect can directly
influence the spin dynamics in metallic ferromagnets.
