Light Eye
From Halopedia, the Halo wiki
The Light Eye is a Glitch on Halo 2 on any level. The glitch can make the lights on Warthog show through the walls as if the walls were foggy windows.
Walkthrough
To perform this glitch you must start any level, and find a point where an Elite, Grunt, or a Warthog with passenger go behind a wall on their own. When this happens, you must save and quit and then restart the game from where you were. Now you must look at the chosen Covenant unit or Warthog and the lights on them should show right through the walls.
- Grunt Lights.jpg
If you look closely you can see the lights on the backs of two grunts and an elite showing through the wall.