After exhausting herself, Madelyn declared "Up!" and pointed to the backpack. Papa obliged, we loaded her in, and he began walking. Whenever he would pause, though, Maddie would say "Boing! Boing!" rather insistently. When he would resume walking she would sort of sing along with every step, very sweetly "Boooing... Boooing... Boooing..." She loves to bounce up and down. And I love her increased ability to express what she wants!