Animal testing involves using animals like rats, mice, dogs and primates to test products like foods, drugs and medical treatments. Around 50-100 million vertebrate animals are used annually, with 90% being rats and mice. Supporters argue it has helped develop important medical advances like vaccines, antibiotics, and surgery techniques. Critics believe it is cruel and unnecessary, that some animals are killed as surplus, and that household products are still tested on animals using methods like dripping irritants in rabbits' eyes. There are arguments on both sides of this complex issue.