The magician shows all sides of a big wooden box.
The front of the box has a big cutout area through which interior of the box is seen to be empty. There are metal bars at intervals from top to bottom of the cutout. The Performer now introduces a balloon and inflates it. He then puts the balloon inside the box and shows the box again.
The Performer now makes a magical gesture. The balloon inside the box pops and magically transforms into a Dove or Rabbit.
Large load area!
Easy to use!