Halo's comical Grunts have been celebrating one birthday or another ever since Halo 2's Grunt birthday party easter egg, which granted players who crashed said party a skull to turn headshots into confetti explosions.

That power lives on in Halo 4, and to celebrate, some Grunts and Jackals in the "Composer" mission hold a dance party behind the glass in the area just before the Chief arrives to hop in a mech.