Determining the sex of animals can be challenging for non-experts, as physical differences are not always apparent. In spotted hyenas, for instance, females have an elongated clitoris that resembles a male's penis, known as a pseudophallus. This structure is associated with fused lips filled with fatty tissue, which are sometimes referred to as "testicles." According to Sarah Benson-Amram, a zoologist at the University of Wyoming, both male and female hyenas have erections during courtship, and the shape of the erect phallus can help distinguish the sexes: a pointed tip indicates a male, while a blunted and straight tip indicates a female. Heribert Hofer, from the Leibniz Institute for Zoo and Wildlife Research, notes that females can also be identified by prominent mammary glands during birth. Additionally, females are generally larger, and their stomachs do not curve upward at the junction of the hind legs as males do. A pink scar from tearing during birth is another indicator of a female. In many animal species, size is not a reliable indicator of sex. For example, in monogamous species like canids or equids, males and females are often the same size. Bright colors or ornaments are typically found in species where males compete for female favor, such as elk or peacocks. However, in species that live in pairs, such as the Cape ground squirrel, there is less competition, and thus less need for visible sexual traits. According to Amiyaal Ilany, a postdoctoral researcher at the University of Pennsylvania, the only physical difference in Cape ground squirrels is that males are slightly larger. However, to distinguish the sexes, one must rely on auditory cues, as males sing to attract females, while females do not sing at all. In some species, such as many snakes and lizards, sexual differentiation is difficult visually. Robert Espinoza, a biologist at California State University in Northridge, notes that snakes may rely more on their sense of smell than visual cues to find a partner. Similarly, many lizards can be nearly impossible to differentiate between males and females. In contrast, some species, like the South American lava lizard, have such distinct differences between the sexes that males and females were initially thought to be different species. In this case, females are colorful, while males are more drab. Some species also change sex during their lives, particularly among fish. For example, rockfish are born female and later become male. Overall, determining the sex of an animal can be complex and requires considering various factors, including physical traits, behavior, and sensory cues.