Penis
Domestic cats have barbed penises, with about 120–150 one millimeter long backwards-pointing spines. Upon withdrawal of the penis, the spines rake the walls of the female's vagina, which is a trigger for ovulation. Lions also have barbed penises. Male felids urinate backwards by curving the tip of the glans penis backward. When male cheetahs urine-mark their territories, they stand one meter away from a tree or rock surface with the tail raised, pointing the penis either horizontally backward or 60° upward.
Common opossum
The common opossum is similar in size to a house cat. The fur of the opossum is actually yellow in the under-fur, but is hidden by the longer black guard-hairs that cover it, while the tail, fingers, and face are lighter "with the tail being without fur, somewhat similar to a giant rat tail." It can measure nearly 20 inches long. It has large ears that are usually black, and its face is usually a pale peach in color, with black whiskers and eyes that reflect reddish in light. With a body length of nearly a foot, and a tail that can reach almost two feet, the common opossum is one of the larger members of its family. An adult can weigh more than three pounds.