Black Ops: What am I doing wrong?

My friend told me that on the map Nuketown in Black Ops, that if you shoot off all the heads of the mannequins, “Sympathy for the Devil” by the Rolling Stones starts playing. I went and did this, went through the entire map and shot off every head of every mannequin, even the ones outside the boundaries. But the song hasn’t played. I just want to know if this is true, or if it is just another Call of Duty myth. And if it is true, then what am I doing wrong?