Plot in The Cask of Amontillado
Nitre is another word for the mineral form of potassium nitrate. This mineral is toxic when breathed for extended periods of time or in high concentration. Poe deliberately gives Fortunato a severe cold for a purpose, as the nitre makes him frequently cough and keeps him from asking a lot of difficult questions about the Amontillado that Montresor might not be able to answer.
In the beginning of the story, Montresor explains that an essential aspect of revenge is for the victim to be aware of the situation. This means Fortunato must become sober enough to understand that Montresor is taking his revenge upon him. Montresor designs his plot of revenge with this in mind, chaining Fortunato up and then allowing him to slowly realize what has happened.
Rheum is a thick watery discharge from the eyes. Poe uses vivid description in this line to emphasize how intoxicated Fortunato currently is. Notice how Poe continues to use Fortunato’s intoxication to help Montresor set the stage for his revenge.
Notice how Poe abruptly ends one scene and opens another immediately in the next line. The reader is given the impression that the two men arrived at Montresor's palazzo with great haste and without any unforeseen problems such as bumping into a common acquaintance along the way.
Poe sets his story during the carnival season in order to give Montresor the perfect cover for his plan. Like everyone else on the streets of Venice, Fortunato is drunk and in a festive mood, which makes him easier to fool. The carnival also distracts the attention of any bystanders who might otherwise notice Monstresor leading Fortunato to his palazzo.
Fortunato knows that Montresor has experience and knowledge with Italian wines to purchase them without expert advice. Given that Montresor is a French name, Fortunado would also likely believe Montresor to not need his help judging French wines. These reasons are why Montresor uses a rare Spanish wine, the prized Amontillado, to appeal to Fortunato’s arrogance and lure him into his snare.
Recall the earlier pun regarding Montresor's status as a mason and as a source of dark humor. When the pun is first presented, drunken Fortunato thinks his friend is being a fool. Now the trowel that he thought of as a joke is the instrument of Montresor's ruthless revenge.
Poe uses alcohol as a plot device throughout the story. In this passage, we learn that Fortunato's obsession with wine allows Montresor the opportunity to take advantage of it. Note how Montresor continues to use wine throughout the rest of the story to achieve his gruesome goal.