Circuses using animals are becoming less and less popular thanks to successful animal advocacy campaigns. The vast majority of circuses using animals employ violent and/or stressful tactics by their trainers who use whips, tight collars, muzzles, electric prods, bull-hooks and other tools of the trade to force animals to perform. Lions, tigers, elephants, bears, domestic animals and others, endure confinement, deprivation and stressful performance schedules. The tricks the animals are forced to learn are done through intensive training with incessant repetition, and unnatural uncomfortable exercises. The animals suffer psychological torment due to confinement and travel, and are often victim to mental illnesses. Circus animals can be killed or abandoned when they become too old or ill to perform. Alternatively, they will be sold to other circuses, private exotic animal collections and even to laboratories for research.