Let’s begin by talking about what a good thesis statement does. First of all, a thesis statement basically lays out your argument for your essay. The thesis statement “clearly delineates the argument that is presented in the work“ and “says what the author or authors are trying to prove” (enotes reference, thesis statement).
In your thesis statement you need to connect the ideas of horror and human. I would write a clear sentence that connects the two.
Poe uses horror for black humor in “The Cask of Amontillado” by describing horrifying events in such an ironic way that they are also humorous.
Irony is when something is unexpected, or the opposite of what is expected. You can read more about irony here: http://www.enotes.com/topic/Irony
Now of course you have to go on to explain this. For example, irony is used when Montressor supposedly worries about Fortunado’s health when he is about to kill him.
“Come,” I said, with decision, “we will go back; your health is precious. (enotes pdf. p 5).
This because even more funny with Fortunado’s ironic answer.
“Enough,” he said; “the cough's a mere nothing; it will not kill me. I shall not die of a cough.” (p. 5)
Fortunado says he will not die of cough. It is funny and horrible, because he is about to die. This is dramatic irony, because “he audience knows the character is making a mistake, even as the character is making it” (enotes reference, irony).
As you read, you can identify other ironic and funny moments, such as when Montressor pretends to be a Mason (p. 7) and when Montressor replies yes, “For the love of God” (p. 8).
Readers often find irony funny, in a black sort of way. This was a common technique of Poe’s.
For more on thesis: http://www.enotes.com/topic/Thesis_statement
For the full text of the story: http://www.enotes.com/cask-amontillado-text
More about irony: http://www.enotes.com/topic/Irony