Kathryn Schulz observes that "One of the strangest things about the human mind is that it can reason about unreasonable things. It is possible, for example, to calculate the speed at which the sleigh would have to travel for Santa Claus to deliver all those gifts on Christmas Eve. It is possible to assess the ratio of a dragon’s wings to its body to determine if it could fly. And it is possible to decide that a yeti is more likely to exist than a leprechaun, even if you think that the likelihood of either of them existing is precisely zero." Walt Disney was a master of making the impossible plausible. Schulz writes, "Walt Disney is best remembered today for his Magic Kingdom, his chief contribution to the art of animation was not his extraordinary imagination but his extraordinary realism. 'We cannot do the fantastic things, based on the real, unless we first know the real,' he once wrote, by way of explaining why, in 1929, he began driving his animators to a studio in downtown Los Angeles for night classes in life drawing." This was part of the Disney revolution: "all those talking mice, singing lions, dancing puppets, and marching brooms began obeying the laws of physics. It was Disney, for instance, who introduced to the cartoon universe one of the fundamental elements of the real one: gravity. Even those of his characters who could fly could fall, and, when they did, their knees, jowls, hair, and clothes responded as our human ones do when we thump to the ground. Other laws of nature applied, too. Witches on broomsticks got buffeted by the wind. Goofy, attached by his feet to the top of a roller-coaster track and by his neck to the cars, didn’t just get longer as the ride started plunging downhill; he also got skinnier, which is to say that his volume remained constant." All this was necessary, Disney thought, to achieving "plausible impossibility."