Eyes of the Serpent

Two Eyes of the Serpent exist on the Serpent Isle: the blue eye of Order and the red eye of Chaos.

Description
Their function is simple: together they can call the Great Earth Serpent in the Shrine of Balance, when being put onto the altar in front of the Wall of Lights. The fate of these two items is quite different.

The Eye of Chaos
The Eye of Chaos was brought to the Isle of Crypts by the forces of Balance in order to hide it from the forces of Order, which were destroying anything Chaos-related. It was years later, when the Avatar needed the Blackrock Serpent of Balance to pass and found the Eye behind a force field just like that without any indication of its use. Dispelling the field, the Avatar took the Eye and later used it in the Shrine of Balance to call the Great Earth Serpent.

The Eye of Order
The Eye of Order was stored in the Shrine of Balance in order to deny Order this powerful artifact, and the Avatar had to put three of the Serpent Artifacts (Staff, Crown, Armour) on the right altar to receive it from the Great Earth Serpent itself. A short while later the eye was used to call the Great Earth Serpent.

Trivia

 * Nowhere in the game are these items ever mentioned, they just come out of the blue and can hit players unprepared.