These pigs had jellyfish genetic material added to them when they were still embryos. During the day, the pigs have a greenish tinge to their skin, and have partially green eyes and teeth. In the dark, however, their entire bodies glow a bright green. Amazingly, not only did this first generation of gene-transplanted pigs successfully glow in the dark, but their natural offspring inherited this ability as well.
(Sources: 1, 2)
19 Totally Incredible Facts