By clipping the camera through a wall in the 6th level "Munition Line", a hidden image of a creepy person can be found. This is an old Internet meme known as "Creepy Ugly Guy", a photoshopped image based on an example photo used in the API plug-in "Kai's Power Goo", that spliced together stock images of a man, a young girl, and a chimpanzee, and is believed to have been spread online as early as 1996 when the software originally came out.