There is an invisible "sensor curtain" around the robots. I accidentally put my camera too far "in" and the robots stopped instantly. As soon as the attendant s

There is an invisible "sensor curtain" around the robots. I accidentally put my camera too far "in" and the robots stopped instantly. As soon as the attendant saw everything was OK (and helpfully explained to me what happened) she pushed a "resume" button on the control panel and they continued right where they left off.