Proceed through the mission until you go up toward a hill to meet a large purple platform containing a good number of covenant around and in it. Drive or walk around the left side of it to meet a dipped down curve with a couple Marines taking cover in it and look for a Warthog. Behind it, look for a Marine talking to another wounded Marine on the ground. Turn up the volume so you can hear the conversation. It sounds like the wounded Marine is talking about being animals in a cage, while the Covenant are the predators. The conversation soon stops after awhile.