The signaling principle basically states that people learn better when cues, letting them know where to focus their attention, are incorporated in the presentation. In animations, this could take the form of labels, arrows or highlighting. In the above example, we explain (in voice-over on the original presentation) how both travelling and standing sine waves produce simple harmonic motion at a particular point. So here the vertical movement at one point along the wave is highlighted by fading the background of all but one of the rods.