The safety of Tasers, the electric pistols that are widely used by police, is under new scrutiny after a study by a Wisconsin scientist showed that shocks from the guns cause the hearts of healthy pigs to stop beating. The finding contradicts previous studies that showed that Taser shocks did not cause heart disturbances in pigs, whose hearts are similar to those in humans. John G. Webster, a professor of biomedical engineering at the University of Wisconsin who conducted the new study, said the earlier studies contained serious errors because they did not account for the fact that pigs have...