Only here [in the Center] a new union can occur, as the Mysterious Pass is the ideal space and time to experience the interpenetrating fluctuations of Yin and Yang. The Mysterious Pass is therefore the primordial Chaos (hundun) containing the germ of life-the pre-cosmic sparkle of Original Yang and Original Yin-which is the prime mover and the materia prima of the alchemical work. - Monica Esposito