In the episode " Choo-Choo! ", Dora and her best friend Boots visit the train station where they meet , a little blue train. Azul is sad because he is the only train without a whistle, and the bigger trains, Big Red and Big Green, often make fun of him for it.
The tunnel is pitch black. Since Azul has no whistle to warn other trains, Dora uses a flashlight from her Backpack to see, and they all whistle together to let other trains know they are coming. In the episode " Choo-Choo
Azul needs a boost to climb the steep tracks. Dora and the viewer help him by cheering "C'mon, Azul!" to give him the power to reach the top. In the episode " Choo-Choo! "