9. Kino Der Toten's Movie Swap & Secret Song (Black Ops)
https://www.youtube.com/watch?v=bOcXB_Kj0BE COD's developers are far more astute than the average gamer gives them credit for, and as such this easter egg's brilliance is twofold. On the one hand the level's name 'Kino der Toten' translates as 'Cinema of the Dead' (a great name for a movie if you're listening, Hollywood), but also because you can actually pick up the film reels dotted about the map and slot them into the projector, changing the clip playing in the lobby. Lastly, if you collect three of the scattered meteor pieces from around the map (discoverable through strange audio cues that'll let you know you're nearby), a song named 115 by Elena Siegman will play. Luckily it's a pulse-pounding death metal-influenced thrasher and isn't proximity-dependant, so throw it on and get to blowing up more zombie heads!