Cats climb curtains, leap onto bookshelves, and tiptoe across windowsills. To survive a misstep, they rely on a real-life superpower: the righting reflex, an ability to fall from any orientation…and still land on their feet. It's a rare skill, only shared with primates, rabbits, rats, and guinea pigs. The motion is too fast to be seen with the human eye, and too fast to be controlled by the cat's conscious brain. As it falls, the cat cannot interact with the outside world and can only change its orientation with internal twisting motions. The righting reflex even works in the dark, which means that a cat can remember the direction of gravity before it falls. As told in Falling Felines and Fundamental Physics, understanding the righting reflex took the development of 200 years of mechanics and neuroscience and the obsessions of an interesting cast of characters.

This book is the first trade science book by Gregory Gbur, a professor of physics at the University of North Carolina at Charlotte. His interests in optics, history of science, and horror fiction all appear in this book. He is most known as an award-winning blogger for his website Skulls in the Stars. Some of his best online work makes a guest appearance in this book, such as a young boy's attempt to make ice cream, and his discovery that hot water freezes faster than cold.

The book proceeds chronologically through the history of the reflex, depicting the state of the art of knowledge of each era, the discovery that changed things, and the eventual fate of the scientists involved. In 1821, painters all assumed that when horses galloped, they lifted their legs simultaneously off the ground. This led to paintings in which horses seemed to be floating in the air. The assumption was only corrected when the photographer Eadward Muybridge invented a high-speed camera to show that galloping horses always have at least one leg on the ground. Purportedly, the discovery threw artists into despair for having painted the horse incorrectly for years. Depicting emotional reactions to the scientific discovery is where the book really excels. The author has a gift for sneakily teaching science history using a gripping story line.

A number of interesting and subtle ideas are discussed in the book, making it a rich educational resource. Examples include the law of conservation of angular momentum, Einstein's equivalence theory of gravitational forces and accelerating reference frames, and the discovery that reflexes go from the sensory organs directly to the spinal cord rather than to the brain. The author easily explains topics varying from physics to neuroscience. Like a patient teacher, the author takes his time to give the background for each of these discoveries, depicting parts of the brain or breaking down Newton's laws. This is one of the author's greatest strength, the ability to teach complex subjects without requiring prior knowledge. I can imagine the book to be used in a high school classroom, where students would read each chapter, and a physics or biology teacher would expand on the concept introduced. Most of the book is written in everyday terms, and only with the geometric phase concept in Chapter 12, did I have to look for external sources for clarification.

The most engaging parts of the book are its beginning and middle, when the author discusses 19th and 20th century physiologists like Etiene-Jules Marey and Giles Brindley. Brindley put rabbits in strange chambers to spin them around before dropping them, demonstrating that it is not the moment of release that tells the rabbits the direction of gravity, but in fact the five seconds before drop. This memory is how the rabbits know which way to perform the righting reflex.

The end of the book feels more rushed and loses the story-telling virtues of the beginning and middle. Here, the author discusses the twentieth century computer software programs and robots that emulate the cat righting reflex. Here, the work is less readable because far too many works are discussed in rapid sequence.

The author meticulously includes 75 illustrations, including reproductions of original photos: Maxwell with his dog, the first ever daguerreotype of a cat from 1840 to 1860, Etienne-Jules Marey's original high-speed photos of cat's falling, and pawprints from the first cat coauthor of a physics paper. The reproductions, which span over 200 years, add to the realism of the book. The author also includes quotes from the scientists and their family members, which gives one the eerie feeling that the long dead scientists have come back to life!

The book covers in graphic detail some of the negative aspects of science. This includes competition between scientists, pettiness, and attempts to claim credit or discredit one another. Aspects of their personal lives are also included such as infidelity and even abandoning their own children. Seeing the personal lives of the scientists, including their successes and mistakes, helped me remember them as actual people. But covering these topics may dissuade younger readers from pursuing science, and unintentionally restrict the book's audience.

Deep down, the book is a tribute to the way science really happens, often by twists and turns, and surprise applications between one field and the other. It's a testament that studying something as mundane as falling cat can push the boundaries of science forward, leading to useful discoveries across disciplines.

David L. Hu is a professor of mechanical engineering and biology at Georgia Institute of Technology, the 2015 winner of Ig Nobel Prize in physics for showing that mammals urinate on average for 21 seconds, and the author of the book How to Walk on Water and Climb Up Walls: Animal Movement and the Robots of the Future (Princeton, 2020).