Hold a posture past the point where it stays comfortable, keep breathing, and the practice starts to move on its own. Small movements happen without you choosing them, and so do images, old feelings, and the urge to stop. Swami Kripalu called this the kriyā of chitta and prāna, and he named both because a practice can feel off balance if one is missing. Kripalu Yoga works with them together, so awareness and energy grow at the same rate and cooperate instead of taking turns.