"Need to make content appear, change or disappear out of order? Need to control the order that things appear while in front of your audience? Playing games? You need to play with PowerPoint's Triggers option for custom animations."
"Let's get past the term, first: A trigger is nothing more than an item on your PowerPoint slide-- it could be a picture, a shape, a button, or even a paragraph or text box-- that sets off an action when you click it. The action might be a sound, a movie, or an animation, such as text becoming visible on the slide."
"Indeed, with the addition of motion paths, new trigger effects and the ability to add two animation behaviors to one object, PowerPoint has become capable of creating sophisticated animations that rival complex animation software."