Scientists have temporarily attached a pig’s kidney to a human body and watched it begin to work. The feat is a small step in the decades-long quest to one day use animal organs for life-saving transplants. Surgeons in New York attached the pig kidney to blood vessels outside the body of a deceased recipient so they could observe it for two days. The kidney did what it was supposed to do and didn’t trigger rejection. Experts say the test done last month paves the way for the first experimental pig organ transplants in living people in the next several years.