Note This will show triggered animations automatically; you do not have to click the item to see it animate.
To preview all animations, including triggered animations, click 
in the Custom Animation task pane.
Note This will show triggered animations when you click the specified item.
TipBy default, a preview of all animated effects on a slide is shown when you apply an animation to an item. To turn this feature off, clear the AutoPreview check box in the Custom Animation task pane.