  Recently, an experiment at GSI Darmstadt has observed oscillating decay rates
of heavy ions. Several controversial attempts have been made to explain this
effect in terms of neutrino mixing. We briefly describe the experimental
results, give an overview of the literature, and show that the effect cannot be
due to neutrino mixing. If the effect survives, it could, however, be explained
by hypothetical internal excitations of the mother ions (~ 10^(-15) eV).
