PETA (People for the Ethical Treatment of Animals) opposes the use of shock collars, stating "Dogs wearing shock collars can suffer from physical pain and injury (ranging from burns to cardiac fibrillation) and psychological stress, including severe anxiety and displaced aggression. Individual animals vary in their temperaments and pain thresholds; a shock that seems mild to one dog may be severe to another. The anxiety and confusion caused by repeated shocks can lead to changes in the heart and respiration rate or gastrointestinal disorders. Electronic collars can also malfunction, either administering nonstop shocks or delivering no shocks at all".