While our eyes gladly look at he famous trompe-l’oeil and other optical illusions, our ears cannot be deprived of such a treat in the heart of the sound universe. This book gives us many keys to it, allowing, for example, to understand why the minor perception of major intervals (or the reverse) can, in certain cases, attest to a subtle and refined listening. Several analogous paradoxes are developed there, along with innovative educational options.