OK. Not sure how much we're going to spoil the video, but let's just say that this particularly intricate easter egg will seem very familiar to Doctor Who fans... 

 

To activate it, run around the Nuk3town map and shoot the arms off of EVERY iRobot knockoff mannequin in under 2 minutes. It's not an easy task unless you know the stage really well (and have a friend to help). Or, just watch this video by TheHiddenBlade01.