"Lee and Yang... suggested that the particle-antiparticle mirror could be flawed. ...[T]wo experiments—by , Leon Lederman and Marcel Weinrich... and by Jerome Friedman and Val Telegdi...—looked at multiple particle transformations in which a pion decays into a , which in turn decays into an electron. ...[These] found that ...[f]or a positively charged pion, the muon's spin points backwards, against its direction of motion. [When t]he antiparticle... a negatively charged pion... decays, the muon emerges with its spin pointing in the direction of its motion. Looking in a mirror that changes particles into antiparticles, the antismoke comes down the chimney."