It's no surprise that some people believe the Earth is flat, but what happens when Tesla CEO Elon Musk responds to a tweet made by "Flat Earth Society" on Twitter? Well, let's just say that hilarity ensues. The most popular flat-earther theory claims that Earth is a disc with the Arctic Circle in the center and Antarctica, a 150-foot-tall wall of ice, located around the rim. They also say NASA employees guard this ice wall to prevent people from climbing over and falling off the disc. Continue reading to see how the internet reacted.