I Find That Highly Logical, Captain

In the "dragger" MC, attached to the button, you will find the following:

on (press) {
    mouseClick=1;
}
on (release, releaseOutside) {
    mouseClick=0;
}

Nothing shocking here. This is just a lazy way of interacting with the control structure of the actual clip. They probably should be function calls, but, oh well.

The centerpiece of the actionscript is the movie - the actions attached to the "dragger" MC. The commenting is thorough, so I don't feel the need to expound. One thing that might not be obvious if you are coming from Flash 4: the onClipEvent handler with the argument enterFrame will execute its contents every time the layhead enters that frame. For a MC with one frame, that means that it will loop continuously, which is a HUGE relief from the Flash 4 2-frame Mickey Mouse construct.

The other thing that is different from Flash 4 is that this script applies to the movie clip as a whole. In other words, it is entered into the Actions window with the MC selected. In F4, you had to open up the movie clip and create a loop with at least 2 frames to get a script that repeatedly tested some conditions.

onClipEvent (load) {
//set the initial rotation of the dinosaur
	to a front view
compare=5;
}

onClipEvent (enterFrame) {
dinoFrame=_root.dino._currentframe;

//user is holding down mouse button
if(mouseClick==1){
	pos=this._x;

//the movie is 320px wide, with 15 sectors total,
//so each one is 16px wide
	sector=int(pos/16) + 1;

//user is moving mouse to the right
	if (sector > compare){
		bigger();

//user is moving mouse to the left
	}else if(sector < compare){
		smaller();
	}

_root.dino.gotoAndStop(dinoFrame);
compare=sector;

//user has let off button
}else{
	_root.dino.stop();
}

function bigger(){
//if the "dino" MC is at the end, start it over
//so it looks like a seamless cirle.
if (dinoFrame == 20){
	dinoFrame = 0;
	}
dinoFrame ++;
}

//and if the MC is at the beginning, skip to the end.
function smaller(){
if (dinoFrame == 1){
	dinoFrame = 21;
	}
dinoFrame --;

}
}

Structuring the Flash Movie
3Dino - Another Approach to Flash 3D
Memoirs, Regrets