The Gravemind cut scene shows the idolatry of the Grunts.
When I first heard about this one, I thought that it was a fake egg, but it turns out that it’s real. At the beginning of the Gravemind level, there is a cut scene with a group of dancing Grunts in the background. With the grunts is some sort of poster. If you look closely, you’ll see that it’s a cardboard cutout of a guy lifting his shirt (see Figures 3-1 and 3-2).
All you have to do to see this egg is start a Legendary difficulty game on the Gravemind level. You do not have to play any of the level or play any of the previous levels on the Legendary difficulty setting. When the cut scene begins, watch the back of the room—you’ll see the circle of Grunts. The little guys are clearly dancing with something.