Grey is a paraplegic and only has control of his head and neck. Until the very end, STEM can control the rest of him but not his head or neck. Throughout the film, the fight scenes reflect this division. Grey is constantly reacting in horror and not looking at the violence that his body is dealing out. In the fight with Serk, STEM moves Grey's face aside with Grey's hand to dodge a knife slash because STEM can't move Grey's head directly. When STEM asks for help during the fight with Fisk, Grey headbutts Fisk, something STEM could not have made him do.
