|“||It betrays me!||”|
|— Constantine, dying|
This is the booby-trapped counterfeit of The Eye. It was crafted by the Hammerites and given to Garrett previous to the TDP/TG mission "Into The Maw Of Chaos". If put in place of the real Eye, it will explode into a square of magical energy, killing Constantine at the conclusion of his spell.
Oddly enough, the switch does not actually need to be made before The Eye is activated. In order to give Constantine time to finish his soliloquy, "It is done! The rule of the mansy stone blind fools falls to me!", the game continues for a while before the mission is officially failed. Even if spotted, Garrett should survive long enough to finish the last objective. The result is the same as a normal success, but without the satisfaction of seeing the overdramatized "dying" performance.