The Oscar-winning visual effects of last year's film Interstellar were out-of-this world. But one of the coolest parts were the robots TARS and CASE, which actually existed in real life and weren't the results of CGI magic.In this behind-the-scenes feature, director Christopher Nolan said he wanted "articulate machines" rather than robots because those are just machine impersonating a human being."These are purely machines," he said referring to TARS and CASE. "They have personality though, they have intelligence and physicality."To obtain those human-like characteristics, TARS was manned by a puppeteer. In the final edits, CGI was only used to do things that a human couldn't do. Nolan said he was looking for someone to give the robot "life and personality" to the inanimate object, so the job appropriately went to Sesame Street puppeteer Bill Irwin.The originally light-weight aluminum puppet, if you will, needed to be stainless steel because it looked more like TARS. Unfortunately for Irwin, it was a 200 pound piece of hulking steel that proved to be quite a challenge.After watching this nine-minute clip, even we were exhausted on Irwin's behalf.