The image on the right, courtesy of Futility Closet, is one of the most unique images one could possibly find from the score to Chopin’s Étude No. 5, Op. 10, perhaps best known as the “Black Key Étude.”
Why unique, you ask? Well, as FC points out in the original post, “the red F is noteworthy because it’s the only point in the whole composition that the right hand touches a white key – apart from that, it plays black keys exclusively.”
Now, if I could just figure out how to use this fantastic website of Chopin’s Complete First Editions Online, (and if I could sight-read music with any degree of competence), I could tell you at what point to pay attention during the following YouTube clip to hear the “odd man out,” which occurs in measure #66.
Orthodox. Faithful. Free.
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Here’s Vladimir Ashkenazy (one of my favorite Chopin interpreters) playing the étude in question, which is dazzlingly difficult for my “took piano for just long enough to be dangerous”-level piano-playing mind: