Until the day comes when all vehicles are fully autonomous, self-driving cars must be more than safe and efficient, they must also understand and interact naturally with human drivers. The web extras include videos demonstrating "rude" behavior by Tesla's Autopilot system, www.youtube.com/watch?v=el4OdwtgzNk; a human driver confused by self-driving technology, www.youtube.com/watch?v=Uj-rK8V-rik; and aggressive driving prompted by self-driving technology, www.youtube.com/watch?v=FbSQm3YaAzA.