 Pairs of photons have been the most common physical systems in Bell tests because they are relatively easy to produce and analyze, but there have been experiments using other systems. Lamehi-Rachti and Mittig (1976) measured spin correlations in proton pairs prepared by low-energy scattering. Their results agreed well with the quantum mechanical prediction and violated Bell’s Inequality, but, as in the positronium experiments, strong auxiliary assumptions had to be made. 