From Halopedia, the Halo wiki
Retrieved from "https://www.halopedia.org/index.php?title=Light_Eye&oldid=1297535"
To perform this glitch, start at any level and find a point where a Sangheili, Unggoy, or a Warthog with a passenger goes behind a wall on their own. When this happens, you must save and quit and then restart the game from your saved position. Now you must look at the chosen Covenant unit or Warthog and the lights on them should show right through the walls.