Jigglebones move when their position changes. The "bones" of a model exist in a hierarchy. This hierarchy starts with the root, which has many child bones. The pelvis usually has a chest bone as a child, which in turn has another chest bone as a child, which in turn has the breasts as children. When you move the pelvis, the chest and any of its children will move as well. So when you move any body part that also changes the position of the jigglebones, they will animate to assume that position.