Inhumane treatment of animals takes on various forms. Domestic and captive animals often live in inhumane or insanitary conditions. This is the case in many zoos. Unfit domestic animals can be abandoned or painfully put death. In some countries, the surplus of dogs is controlled by the use of strychnine. There is wanton abuse of animals for man's convenience, namely for the claims and interests of science, sport, entertainment and the production of food. Inhumane slaughter of food animals is still widespread in the meat industry and in the whaling and sealing industries. The cramming of geese is but another example of cruelty inflicted on livestock. Cruel transportation, whether by road, rail, sea or air, is one of the main causes of animal suffering.
Contemporary philosophers question the traditional legitimizing of tyranny of human over nonhuman animals. Thomas Aquinas, in denying that animals have souls, laid the theological groundwork for post-Enlightenment philosophers to dismiss the non-human side of creation altogether.
A clear link has been established between the abuse of children, adult aggressiveness and cruelty to animals. Three quarters of the aggressive criminals interviewed in one study were abused and beaten as children (as compared to only ten percent of non-criminals). Sixty percent of this group committed cruelty to animals. One man put his girlfriend's cat into a microwave oven. Generally the motivation for these acts ranged from a desire to shock or to satisfy a grudge against another species to a displacement of hostility from a person whom the criminal did not attack to the animal which he could.