Reading a book on the NOOK Tablet is more than a text-based experience; you can enjoy videos embedded in books, too. When you come across a video, tap its triangle to play it. Control the video using the usual controls at bottom for stopping and resuming, and dragging the bar to go forward or backward.
If you’d like to see the video taking up the full screen, tap the icon that has four outward-pointing arrows. You’ll see video controls for a few seconds, but then they vanish. To make them reappear, tap the screen. To get back to the page you were just reading, tap the Back button at upper left.