Play on "Halo" in Campaign mode with two players on the same Xbox 360. After you leave the control room, follow the snowy path off to the right. Cortana will tell you to find a door. It is easy to find as it is very large and the path leads directly to it. Once you pass through the door, go down the hall and fight off the Flood. Leave player two at the end of the hall you just came through while making sure not to look at the door you just came in. Have player one progress as usual. When player one enters the hallway that leads to the rest of the mission, have player two look at the first door you came through. It should show player one's screen in the doorway. If you leave the hallway, it will change into a normal door.