The Smart Action Tunnel Pack is just that – tunnels that bring action to your Smart Tech train from BRIO. When the train passes through the tunnel, it makes the engine sound and act according to the BRIO tunnel icon: the turtle results in the engine making choo-choo and braking sounds while slowing down; the rabbit speeds it up again. BRIO Smart toys are preferably used with BRIO Smart train to make sounds and actions possible.