On quarintine zone on legendary co-op as soon as u start the level turn around u should see a tunnel. head through it, turn left u see a broken snipping lift jump over it turn left a little keep walking u see a ledge crouch, walk onto it, head down it yu'll see a skull (looks like a flood far away.) pick it up (hold X) and congrats u sucsesfully got the spuntnik skull. it's efect is mele and grenades are more powerful!!! yur welcome ;D