Can you identify humourous elements in the story "The Cask of Amontillado" and what does the humor add to the story?

Any humor in Poe's "The Cask of Amontillado" is dark
humor, indeed.  I can only tell you what I have found amusing when I read this story. 
I'm always a little amused when Montressor says he told his servants he wouldn't be home
until the next day but expected them to be there to do their jobs--knowing full well
they'd all take off for Carnival.  I also enjoy the picture Poe draws of Fortunato in
his crazy "parti-colored" jester-like outfit.  It's slightly amusing to see Fortunato
get lured into the catacombs, though it's not funny to think of what happens to him
there.  Finally, I always like the picture of Fortunato giving secret Masonic signals to
a very confused Montressor.  These are not, as I said, wildly comical; instead, they are
amusing incidents in a very dark work.  If the humorous elements were truly outrageously
funny, it would clash dramatically with the somber and melancholy tone found in the rest
of the work.  These moments are a perfect accompaniment and contrast to that darkness, I
think, and each of them serves to advance some dramatic element of plot in the
story.