In chapter eight, The Art of Flash Animation begins with a discussion of symbols, and rambles on to more topics that have nothing to do with the chapter title, but still add to the skill set that you are developing. Mr. Smith is an unusual writer. His explanation of symbols leaves something to be desired, so I have given you the link above for more information about them.
The text gives us a method for making a piece of a drawing into a symbol:
Mr. Smith seems taken with symbols because he can transform them with a right-click. The Free Transform option of the right-click menu lets you rotate symbols, resize (scale) them, and skew them. You can resize them on the x-axis, the y-axis, or both. (This interface is two-dimensional.)
Note that the mouse pointer takes on a different shape each time you are able to perform a different action with the Free Transform tool.
Mr. Smith starts an exercise on page 300 that runs to page 311. You should walk through this exercise in class, paying more attention to his instructions than to his anecdotes.
In the course of the exercise, Mr. Smith introduces Tweening. In short, he sets a series of keyframe locations for an object. As he does, Flash determines where the object must go in between each of the keyframes. At the end of the exercise, Mr. Smith also makes a few good observations about thinking about real life when setting animation movements. As he said earlier in the text, the hardest thing to animate is something the audience knows well. People know how eyes move. Think about real eye movement when you set the keyframes in this exercise, and you can make it more believable.
A new exercise begins on page 312. Before you start it, read the notes on that page. It his inimitable style, Mr. Smith gives you necessary instructions on how to do something after he has already asked you to do it. (I hope he does not teach driver education.)
As the lesson continues, you will create a new layer for a character's torso, another for an arm, and place an arm symbol on the arm layer. You use the Rotate tool with the arm symbol. In order to do so, you will change the location of the arm's pivot point, which Mr. Smith calls a registration point.
In his material on animating the character's legs, ignore the joke about going to the next chapter. You make more layers, cut a leg from the torso layer and paste it on a new leg layer. You should now have the idea that Mr. Smith wants there to be a separate layer for each scene element he wants to animate separately from any other element.
The current lesson continues to page 320, where there is a new heading. The new heading really just continues the animation lesson, but it lets us consider pausing for breath. Make sure to take a break now and again.
As he moves character layers about to show and hide movement to his satisfaction, Mr. Smith also observes that having put a Hanna-Barbera tie on his character has actually put a hole in it. He solves the problem by adding a color fill to the tie. Make sure you do the same.
On page 326, we add a background layer to the scene, which will be used to give the impression of movement across the stage.
On page 330, Mr. Smith adds to our vocabulary. An instance is defined as one particular copy of a symbol from our library. This is a useful concept. We don't have to draw a new symbol each time we want a new tree: we can just place a new instance on the stage. In Flash, we can modify each instance of a tree symbol, making them look different from one another.
Why do we want instances? Even though we can make changes to instances that do not affect each other, we can make a change to the original symbol that will affect each instance of it. This lets us update all instances at once. Be aware that for this trick to work, you have to make the original object into a symbol before you make any copies of it.
The chapter turns to a related topic: shape tweening. Unlike the rest of the chapter, shape tweening is not used on symbols. It is used on vector graphics, so it is best used on simple shapes you make in Flash itself. As with the other tweening lessons, Mr. Smith talks about deforming a simple shape and using the Flash interface to create in between images that flow from one state of the object to the next.