The provided text details a scientific study investigating the detection thresholds of iron and copper salts, specifically how retronasal smell contributes to their perception. Researchers determined these thresholds with and without nasal occlusion, using a modified forced-choice ascending method of limits and various statistical analyses. The study found that nasal occlusion significantly increased detection thresholds for both iron and copper salts but not for sodium chloride, suggesting that a retronasal olfactory component is crucial to sensing these metallic compounds at low concentrations. This research implies that the common "metallic taste" associated with these substances is largely an olfactory sensation, potentially arising from lipid oxidation products generated in the mouth.