In many forms of storytelling the hero has to overcome many trials in order to emerge victorious. One example would be the story of Jonah from the old Testament. He had to be swollowed by a whale to become a prophet. In video games the hero is usually beset by overwhelming adversity, it is only a small strech of the imagination to see him or her as being chewed up and digested- hense the digestive images. Another potental interpitation is that these tunnels are not a digestive track but a birth canal. This comes to mind when the hero from Gears of War 2 emerges from the hole covered in blood. Death and rebirth are frequent archetyes in mythology. Often the hero symbolicly or literaly dies and is reborn. These types of images could come from either source of perhaps a combination of the two.