Masquerade is a form of camouflage in which animals use their body size, shape, and coloration to resemble inanimate objects in their environment to deceive predators. However, there is a lack of experimental evidence to show that animals actively choose objects that match these body parameters. To explore how the Hainan four-eyed turtle, Sacalia insulensis, masquerades using suitable stones, we used indoor video surveillance technology to study the preferences of juvenile S. insulensis for stones of different sizes, shapes, and colors. The results indicated that under normal conditions, the turtles preferred larger oval or round brown stones. When disturbed (swinging the arm of a researcher back and forth above the experimental setup every hour to mimic a predator), the turtles showed a preference for brown stones that were closer to their size and oval in shape. These findings suggest that juvenile S. insulensis prefer stones that resemble their carapace size, shape, and color to masquerade when undisturbed, and that this preference is reinforced when they masquerade to reduce the risk of predation. To the best of our knowledge, this is the first study to provide evidence that vertebrates can recognize object shapes and selectively choose objects that resemble their own shape for masquerading to reduce predation risk.

Animal camouflage serves the dual purpose of enhancing predation or anti-predation efficiency through strategies such as background matching, disruptive coloration, countershading, masquerade, and motion dazzle. Although body size and shape determine the visual appearance of animals, potentially affecting their camouflage effectiveness, research over the past two centuries has primarily focused on animal coloration. Over the past two decades, attention has gradually shifted to the impact of body size and shape on camouflage. In this review, we analyze the impact of animal body size and shape on camouflage based on existing research and identify research issues and challenges. The results of existing studies indicate a negative correlation between background matching effectiveness and an animal’s body size, whereas flatter body shapes enhancing background matching. The effectiveness of disruptive coloration is also negatively correlated with body size, whereas irregular body shapes physically disrupt the body outline, reducing the visibility of true edges and making it challenging for predators to identify prey. Countershading is more likely to occur in larger mammal groups with smaller individuals, whereas body size is unrelated to countershading in smaller animal groups. Different body shapes also contribute to variations in countershading effectiveness. Animals employing masquerade achieve camouflage by resembling inanimate objects in their habitats in terms of body size and shape. The camouflaging effect of motion dazzle is negatively correlated with body size; however, the impact of body shape on motion dazzle remains unknown. A significant research gap exists in examining correlations between various camouflage strategies and body size and shape. Further, insufficient exploration of these strategies warrants thorough investigation in the future to better understand the mechanisms and evolutionary factors influencing camouflage in animals. Our review provides a theoretical foundation for the development of novel camouflage strategies.