What foreshadowing can be seen when Montresor ensures the secrecy of his actions?

Foreshadowing is a warning or hint of an event that is going to occur later on in a story, movie, or novel. In "The Cask of Amontillado," Poe uses foreshadowing by suggesting something very bad is going to befall the clueless Fortunato. We learn in the first paragraph that Fortunato has injured Montresor in unspecified ways and that Montresor has revenge in mind. This warns the reader that revenge will be central to this tale. Other instances of foreshadowing include the fact that Montresor's servants are all away partying during the Mardi Gras, leaving his house empty and leading the reader to wonder why Montresor doesn't want anybody around. Secresy, including taking Fortunato deep into the catacombs, far from any human eyes, makes us nervous about what Montresor has in mind. We don't do evil deeds before witnesses, if we can avoid it. Further, once they are in the catacombs, Montresor, knowing his "friend" will refuse, urges Fortunato to "go back before it is too late." He seems, in the moment, to be responding to Fortunato's cough, but the ominous words "before it is too late" hint that Montresor has a plan in mind. The fact that the two lead characters are surrounded by the bones of dead bodies foreshadows death.
All through the story, Montresor suggests that he is going to do something terrible, and the end of the story does not disappoint. At the end, we might be shocked, but we probably are not surprised: Poe has given us enough indications of Montresor's intentions that the fantastic murder is believable to us.