The saying “cats have nine lives” originated from ancient times, filled with humor, imagination, and mystery, but it actually contains certain principles of mechanics. This article organizes and explores various mechanical explanations throughout history on this issue, categorizes them into four interpretations: the limbs opening and closing theory, the tail rotating theory, the doubleaxis rotation theory, and the spine bending theory, all of which are based on conservation of angular momentum. Although these explanations have their shortcomings, overall, they provide a more scientific basis for this ancient saying. Through indepth exploration, we hope to make people realize that mechanics, as one of the earliest branches of physics, is closely related to human life, offering a scientific way for people to deeply think about and explore natural phenomena. The principles of mechanics not only explain the marvels of cats, but also remind us of the ubiquitous mysteries of science around us, looking forward to people gaining a deeper understanding and exploration of the laws of nature.