def _get_reference(self):
        """
        Sets up references to important components. A reference is typically an
        index or a list of indices that point to the corresponding elements
        in a flatten array, which is how MuJoCo stores physical simulation data.
        """
        super()._get_reference()
        self.cubeA_body_id = self.sim.model.body_name2id("cubeA")
        self.cubeB_body_id = self.sim.model.body_name2id("cubeB")
        self.l_finger_geom_ids = [
            self.sim.model.geom_name2id(x) for x in self.gripper.left_finger_geoms
        ]
        self.r_finger_geom_ids = [
            self.sim.model.geom_name2id(x) for x in self.gripper.right_finger_geoms
        ]
        self.cubeA_geom_id = self.sim.model.geom_name2id("cubeA")
        self.cubeB_geom_id = self.sim.model.geom_name2id("cubeB")