I reckon its an ability of the EMS. He prob is in Spirit form which allows him to move at speed of light and also allows things to pass through him. I mean why would the First thought that he had died? If his soul (so to speak) left his body, then it would explain this. Then there's his interest in Itachi and Sasuke. I think he wants to do what Orochimaru wanted to do, take over Sasuke's body, but he needs that body to have EMS for him to become human again. What do you guys think?