We prove an explicit reciprocity law for the Euler system attached to the spin motive of a genus 2 Siegel modular form. As consequences, we obtain one inclusion of the Iwasawa Main Conjecture for such motives, and the Bloch-Kato conjecture in analytic rank 0 for their critical twists.Todas las artes tienen en común el esfuerzo de dominar la materia, de reordenar el caos.