Technical details: All the sounds load and start playing at startup, but the volume is turned all the way down. When you mouse over a ball, its volume increases. If you drag it around the screen, the volume gets louder as the ball gets closer to where it belongs. To create some semblance of perspective, I also made the images larger as they approach the bottom of the screen (the foreground). If you drop the ball (and let up the mouse) in the wrong place, nothing happens, but if you put it in its home, then it plays the last frame of the movie clip, which is the appropriate image, and becomes un-draggable.
When all the clips are in the right place, then a congratulatory message comes out of hiding, and the time elapsed is displayed.