Dumpster Kick Easter Egg
In Mission 6: Only Human, at the first Ceph Anti-Air waypoint, crawl underneath using the underground tunnels to reach an area below the battery, with Ceph enemies. Enter stealth mode so you do not alert the Ceph. Watch for one of the Ceph leaving the enclosed area to stand near a cliff's ledge with a strategically placed dumpster nearby. Then, power kick the dumpster into the waiting Ceph. If done correctly, the Ceph will go flying far into the distance, and you will hear a roar of applause. Psycho's voice can then be heard saying, "That's how you do it!"