The author Edgar Allan Poe had a problem with the dialogue that would go on between Fortunato and Montresor on their long journey through the catacombs. This is why he gave Fortunato a cold and a bad cough. Poe even used a line of quotes consisting of tthe single sound "ugh" just to show how bad Fortunato's cough is. The cough is to prevent him from asking too many questions. He would naturally be expected to ask where Montresor bought the wine, when did he hear about it, how much he paid for it, whom he bought it from, and other related questions. Montresor would have had a hard time lying repeatedly without arousing Fortunato's suspicions. This is also why Poe has Montresor keep Fortunato drinking. Fortunato consumes the lion's share of two bottles of French wine en route to the nonexistent Amontillado and his doom. The only subjects they talk about are Montresor's coat of arms and about the Masons. Montresor gets a little tipsy himself from sharing some of the wine with his intended victim. That is why he behaves in a somewhat zany manner, showing the trowel and claiming to be a Mason. Chances are that Poe did not really know much about Amontillado except that it was a gourmet Spanish sherry. This would be another reason why he wanted to give his character Fortunato a cold and a cough to avoid a lot of discussion of Amontillado. There is actually hardly any significant dialogue between the two men from the time they meet in the street until Montresor has succeeded in chaining Fortunato to the granite wall.
As they walk into the catacombs, Fortunado begins coughing.
Fortunado even says:
“Enough,” he said; “the cough's a mere nothing; it will not kill me. I shall not die of a cough.”
This is an example of foreshadowing, because he does die at the end of the story.
This is also ironic because the narrator gets him to drink, because he’s so concerned about the cough. He is tricking Fortunado into trusting him and letting down his guard.
As they continue, they discuss the vaults and the wine that is supposedly found there. The most significant part of the conversation is not actual conversation, but Montressor’s thoughts. He is planning to get revenge on Fortunado, even while pretending they are the best of friends.