[문 12～문 14] Several years ago, a research scientist wanted to prove that acupuncture didn't really stop pain. He believed that acupuncture worked mostly on the mind, reducing pain only if people believed it would. For his experiments, therefore, he used animals. ____________, animals treated with acupuncture registered little or no response to pain. Researchers later discovered that acupuncture causes the brain to release chemicals called endorphins that block pain in animals as well as humans.