ActionScript 3.0 :: Play Movie Clip On Button Click?

I have been using flash for a while, but AS3 is a whole new world to me.

I simply want to have a movie (box1) to play when a button (btn1) is clicked.

NOTE: The button is within a movie clip (bulb1) which is within another movie clip (trees).

I tried this, but it just kept replaying the whole animation:

Code:

btn1.addEventListener (MouseEvent.CLICK, onClick);
function onClick( event:MouseEvent):void
{
box1.play();
}