Call it embarrassing, or just plain common sense, but a zoo in Japan just realized why two of their hyenas were not mating, according to ITV.
After four years, the light bulb finally went off when the Maruyama Zoo thought that perhaps the hyenas weren't mating because they were not actually the sex they thought they were.
The two hyenas came from a South Korean zoo in an exchange in 2010. One was a male named Kamutori and the was supposedly a 'female' named Kami.
Turns out, the reason this pair had not reproduced was right in front of them; Kami is actually a male, too.
The Sapporo Zoo conducted a gender test on the two hyenas, and said that because male and female hyenas have similar genitalia, it is "very difficult" to determine the sex just by looking.
Now, the zoo will be looking for an actual female to mate with one of the boys.