dizzyd

Corrected entry: When Vizzini accepts the battle of wits with Westley, Westley states that the poison he has is "called iocane powder. It is odorless, tasteless, dissolves instantly in liquid, and is among the more deadlier poisons known to man." How is that when Humperdinck finds the empty poison packet later on, he identifies it by sniffing it? Pretty clever for an odorless poison . . .

Correction: His precise words are "Iocane. I'd bet my life on it". From the wording, he doesn't actually know for certain, but he's pretty sure. From the evidence of a dead body with no wounds and a vial of odorless powder, Humperdinck is making an assessment that is, in this case, correct.

Tailkinker

Also, it's a good joke that shows Humperdinck to be a smarter villain than Vizzini (who literally bet his life on it and lost).

Correction: He identified the powder not from an odor, but from the complete lack thereof.

dizzyd

Correction: It is just supposed to be a comedic, deliberate "mistake."