What were the signs that Fortundato welcomed Montressor's trick about the amontillado in "The Cask of Amontillado"?
Fortunato thought it was all a game because he was drunk.
It is Carnival, and Fortunato assumes that Montresor is just taking part in the fun. He is too tipsy to evaluate the situation clearly. Montresor shakes Forunato's hand, and seems concerned about his health. His behavior is very disarming.
"As you are engaged, I am on my way to Luchresi. If any one has a critical turn it is he. He will tell me—"
"Luchresi cannot tell Amontillado from Sherry."
"And yet some fools will have it that his taste is a match for your own.
"Come, let us go."
"To your vaults."
This is reverse psychology. Montresor gets Fortunato into the vault by pretending that he doesn’t want him in the vault. This reverse psychology causes Fortunato to practically beg to see the wine. Montresor protests that Fortunato should not go because he has a cough, but Fortunato insists.
Once underground, Fortunato still thinks they are having fun. He laughs at Montresor's Mason joke and does not even realize he is in danger when he is being bricked up. He still thinks Montresor is joking.
Montresor wasn't joking. Fortunato has no idea what he did to Montresor, but Montresor wants to punish him for whatever perceived injury he did.