A Live Zoom Area
The Live Zoom area feature will highlight a piece of your scene, zoom into it and bring it to the foreground and play what is happening in the background in real-time.
In the Design view select the Add a new Zoom Area tool or press (O) and click on the canvas. You will then be shown a screenshot of the scene you are working with; Select the area of the scene you want to zoom in to, when you have your area click the check mark in the top left corner to accept.
When you have created a zoom area in your movie and you activate the Live icon the zoom area will display a live image of what is happening in the background. The zoom area will not show objects added to the scene, but only the raw recording of the scene.
Edit when and how your zoom area will appear in the scene by adjusting it in the timeline.