The Question and Answer section for Poe’s Short Stories is a great resource to ask questions, find answers, and discuss the novel.
Fortunado manipulates him by playing on his (Fortunado's) knowledge of wine. He prays on Fortunado's vanity when it comes to his expertise of wine. Fortunado suffers from the weakness of excess pride and vanity when it comes to wine.
"Oh, you would have laughed to see how cunningly I thrust it in! I moved it slowly --very, very slowly, so that I might not disturb the old man's sleep."
The whole sequence sounds bizzare and surreal. Consider Poe's diction below:
There were arabesque figures with unsuited limbs and appointments. There were delirious fancies such as the madman fashions. There was much of the beautiful, much of the...