The animation playback mode determines how VisIt gets to the next time state after playing until the end of the animation. There are three animation playback modes: looping, play once, and swing. VisIt loops animations by default so once the end of the animation is reached, it starts playing from the beginning. When the animation mode is set to play once, VisIt plays the animation through until the end and then stops playing the animation. When VisIt reaches the end of the animation in swing mode, the animation starts playing in reverse until it gets to the start, at which point, it starts playing forward again. To set the animation mode, click on one of the Looping, Play once, and Swing radio buttons in the Animation Window.