The United States is dealing with a drug shortage - a legal injection drug shortage, that is. In response, states where capital punishment is still practiced are having to come up with new ways of killing people. Earlier this week, Oklahoma announced that it will start using nitrogen gas for all its executions moving forward, making it the first US state to do so. Critics worry that the method is still unproven as an ethical alternative, and that Oklahoma has yet to devise a protocol for the procedure.