After you get Duncan out of the shack you need to clear his mind.
His mind is numb from all the fluff use.
This is the low-spoiler guide for "Clearing Duncan's mind" puzzle in Nine Noir Lives. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.