Bungie claims a former artist plagiarized work of an indie designer that got included in Marathon's alpha tests.

It's still there and shows up when a programmer forgets to specify a texture." I assume I must have seen these cave pearls many times: I've played a lot of Unreal Engine games, and whoever messed ...

The "beyond Half-Life 2" line is on the money⁠—I don't recall seeing ... but more likely, the game was trying to load textures you didn't technically have access to—if you owned Half-Life ...