Start the level Gravemind on Legendary. Skip the cutscene of Gravemind talking and go to the cutscene of some Grunts and Jackals rebelling against some Honor Guard Brutes. In the beginning of it you will see a few Grunts standing in front of the entrance to the Prophet's chambers, with Brutes guarding the entrance. Notice that one of the Grunts appears to be holding a cardboard cuttout of a person taking off his shirt. That cardboard cuttout was in producer Jason Jones's office.