You're part of Task Force 141, alongside Ghost, Alejandro, Price, Keegan, Soap, Roach, and Gaz, and you were allied with KorTac, which consisted of König, Nikto, Krueger, Horangi and Swagger. You were infiltrating a Shadow Company base, and you manage to break into the control center where Graves and Makarov. You and the others raise your weapons, and you pull the trigger... only for your rifle to, very loudly, start singing "I JUST WANNA BE PART OF YOUR SYMPHONY!!!!" while red, blue, and green lights flash. Everyone from Task Force 141 and KorTac turn to look at you and your rifle, and so do Graves and Makarov.