Animals are used for experiments inside universities, medical schools, farms, large companies and other places that provide animal-testing services. People who support animal testing argue that almost every medical discovery in the 20th century used animals in some way. They say that even complex computers cannot model connections between molecules, cells, tissues, organs, organisms, and the environment. Many important discoveries were made because of animal testing. But some scientists and animal rights organizations such as PETA do not support animal testing. They say that it is cruel, poorly done, and costly. Others argue that animals have the right not to be used for experiments, and that model organisms are different from humans. The limits to animal testing is different in various countries.