Carnival
Carnival is a celebration of freedom and life. This being the setting to our story is ironic because, as we know, not only is Fortunato trapped in the end, but he eventually dies, as well.
Jester Costume
On a very basic level, the costume choice of Fortunato holds meaning, he does end up fooled be Montresor. There is more to it than that, though. In many Shakespeare works, and works during that time, the "fool" is actually the character with the most wits and wisdom. This also holds true in The Cask of Amontillado. Though, he does get duped into following Montresor into the catacombs, and his eventual death, right before he dies he takes away all satisfaction from Montresor. He knows that Montresor wants acknowledgement of Fortunato's alleged injustice, but instead of responding to Montresor he simply rings his bell in the dark of the catacombs. This is shown under the "Example Videos" tab. The scene starts at about 22:45 in the first video.
The Bell
Just before Montresor places the last brick into the wall, Fortunato halts his pleas and screams. Montresor panics as Fortunato does nothing but ring the bells on his costume.
These bells represent more than just a lack of verbal response; the also prove that Fortunato has won. By not acknowledging what he has "done wrong" Fortunato takes away Montresor's revenge.
These bells also represent what Fortunato has been reduced to. He no longer is a loud force, instead he is the haunting jingle of bells that echo through the corridors of the catacombs.
These bells represent more than just a lack of verbal response; the also prove that Fortunato has won. By not acknowledging what he has "done wrong" Fortunato takes away Montresor's revenge.
These bells also represent what Fortunato has been reduced to. He no longer is a loud force, instead he is the haunting jingle of bells that echo through the corridors of the catacombs.