Final answer:
Montresor's premeditated revenge in 'The Cask of Amontillado' is evident from his early narrative where he speaks of the careful planning to avoid punishment, as well as from the actions and conversations leading up to and including the entombment of Fortunato. The revelation of a trowel signifies the depth of Montresor's planning.
Step-by-step explanation:
We know that Montresor planned his revenge in The Cask of Amontillado based on his own words at the beginning of Edgar Allan Poe's story. Montresor clearly states that he had borne the thousand injuries of Fortunato, but upon Fortunato's insult, he vowed to seek revenge.
Furthermore, it is evident that he planned the revenge carefully, as he mentions, 'At length I would be avenged; this was a point definitely settled.' This statement shows determinism and premeditation.
The way Montresor lured Fortunato with the promise of Amontillado during the carnival season and the fact that he had a trowel ready to wall up Fortunato also indicates the level of planning involved in carrying out his plan without risk of punishment.
Much of this planning is subtly revealed through Montresor’s conversation with Fortunato, his calculated actions, and the hints he drops about his family's motto and coat of arms, all of which are preparations for the methodical and sinister enactment of his revenge.
For example, when he produces a trowel from beneath the folds of his cloak, it signifies his readiness to seal Fortunato's fate in the catacombs, under the guise of inviting him to taste a rare wine. This undertone of premeditated malice sets the story’s mood to be one of chilling suspense and horror.