So Westley is Buttercup's one true love...
Not sure if this isn't obvious but
SPOILER AHEAD
The one she has "loved more deeply than a killer like (Westley before her) could only dream of"; "with eyes like the sea after a storm"
...and yet she didn't recognize his voice while blindfolded, or his eyes (like the sea) through his mask, or the lines of half his face (mouth) visible, until he utters the magical servant's line: 'As You Wish' ?
LOL.
Don't get me wrong, I love this movie. But that part always gets me as a little "odd".