The etude by Gyorgy Ligeti I would like you to pay attention to is the second one. It starts at 2'15".
Here is what a competent source has to say about the work:
The third etude, "Touches bloquees" ("Blocked Keys"), uses the same technique that first appeared in "Selbstportrait," the second of the Three Pieces for Two Pianos. Certain keys are held down silently with one hand while the other hand plays a very fast chromatic line on and around the blocked keys, which of course do not sound. The result is a complicated rhythmic pattern that gives the music a somewhat mechanical quality. At first the silent gaps are all the duration of a single eighth, but eventually the gaps are two eighths, then three, and continue to increase in length until the texture becomes increasingly sparse. Again, this etude is about the creation of illusion; we see a continuous pattern of eighth notes on the page, but what results in performance are quirky rhythmic patterns that are not discernible to the eye and would be all but impossible to notate in a more traditional fashion to achieve the desired effect.Actually, it wasn't so much about the listening for me. What put me in a state of awe was the seeing. It is the clear struggle between the hands, the tension between the immobile one and the one that runs crazily above it or under it. Also, the tension of the one that is supposed to stay immobile, simply blocking some keys, but cannot resist the opportunity and spurts out sounds now and again, as if to underline it has total power. And then they switch. And we hear it, we hear this body negiation, we hear it once we see it, once we understand the game, it becomes obvious.
The music becomes obvious. Because it's about music, right?
And the soldier-fingers, constantly attempting to design the space through movement. A movement whose purpose is not something else - like a sound - is a dance. If you ever needed proof, here is one.