In act 2 solid sun, after defeating laughing octopus you are faced with the task of tracking Naomi. After tracking her for approx 10 mins you will see her handkerchief on the ground. From here head forward and follow the path, after taking out the squatting guard keep following the path until you see a crop circle in the grass. If you stand there long enough you will hear Colonel Campbell retell the story of his "abduction," something that could be heard toward the end of mgs2 when the virus in the GW starts to affect raidens nanomachines.