To no one's surprise, Exo Zombies mode in Call of Duty: Advanced Warfare has some Easter eggs.
The first Exo Zombies Easter egg, of surely many more to come, has been discovered. It's a musical one that involves Richard Wagner's Ride of the Valkyries. How you unlock it is not as convoluted as you might think.
To trigger this Easter egg, you'll need to touch three objects in the first map, in any order.
Explaining it with text wouldn't be very elegant. So instead, I am going to let YouTuber NoahJ456 do that for you through the magic of video.
Notice how the music starts playing each time he touches one of the objects.