Japanese zookeepers have discovered why their attempts to mate the two polar bears at the Kushiro city zoo have failed: Both are female. When Tsuyoshi, a supposedly male 4-year-old polar bear was introduced to Kurumi, the zoo's 11-year-old female, "he" failed to make any advances. "One day we realized that the two bears urinate in the same way, and we thought, is that how males do it?" said zookeeper Masako Inoue. The sex of polar bears is often difficult to determine because of their long hair. Despite the zoo's breeding plan, it will keep Tsuyoshi, who has become immensely popular with zoo visitors. [CNN, Reuters]