There is normally no need to employ invisible shapes to pick up user interaction. It just turned out to be practical in this situation because I wanted different images of the parrot to appear depending upon where you rolled over it. One of the main things that you need to understand is how the rollover interaction works. It means that the cast member of sprite 3 is swapped for another cast member. Note that there is no need to have both different images in the score.
Director can simply swap one image for the other on the fly.
Rollover of the shapes also causes a sound to play and changes the text of the sprite in channel 12. All of this is happening at the level of lingo rather than through changes in the score. When you click on the wholeParrotShape, however, something does happen in the score. It actually checks to see whether the sound in sound channel 1 is finished. There are many other ways of accomplishing the same thing in Director, but this should provide you with an effective model for your own work.