Complete the Nursery level "Dionaea" with a silver medal or higher rank to unlock the duck. Go to the main menu, select "Laboratory", select "Mode" then select the duck. Place the duck save the game. The main menu animation will drop the liquid and will push the duck, causing it to quack. Note: Because the duck quacks on impact, it is better to place it above ground. Consider using the top of the screen. When you play the animation, it will fall to the ground and quack on impact.