  We report inelastic neutron scattering measurements that provide a distinct
dynamical "fingerprint" for the multiferroic ground state of 3.5% Ga-doped
CuFeO_2. The complex ground state is stabilized by the displacement of the
oxygen atoms, which are also responsible for the multiferroic coupling
predicted by Arima. By comparing the observed and calculated spectrum of spin
excitations, we conclude that the magnetic ground state is a distorted
screw-type spin configuration that requires a mechanism for magnetoelectric
coupling different from the generally accepted spin-current model.
