Deep, dark and sometimes overwhelming, the human compulsion to seek revenge is a complex emotion that science has found incredibly hard to explain. Despite popular consensus that "revenge is sweet," years of experimental research have suggested otherwise, finding that revenge is seldom as satisfying as we anticipate and often leaves the avenger less happy in the long run. New research is adding a twist to the science of revenge, showing that our love-hate relationship with this dark desire is indeed a mixed bag, making us feel both good and bad, for reasons we might not expect.