  We demonstrate that one can use the occurrence of charge symmetry breaking as
a tool to explore the eta--nucleus interaction near the eta threshold. Based on
indications that the cross section ratio of pi+ and pi0 production on nuclei
deviates from the isotopic value in the vicinity of the eta production
threshold, due to, e.g., pi0-eta mixing, we argue that a systematic study of
this ratio as a function of the energy would allow to pin down the sign of the
real part of the eta-nucleus scattering length. This sign plays an important
role in the context of the possible existence of eta-nucleus bound states.
