More than 10,000 reptile species in every shape and size scurry and slither across Earth, from garter snakes to crocodiles — and their nether regions are just as wildly varied.

From spiky penises to multiple penises—or none at all—reptiles have some of the most unusual mating gear on Earth. (Learn how lizard genitalia became a black-market craze.)

Most of the current knowledge of reptilian genitalia focuses on male parts, but scientists are turning more and more to the study of their female counterparts—it’s just a bit trickier since female parts are situated inside the animal.

Snakes and lizards have not just one, but two penises, called hemipenes.

University of Sydney researcher Christopher Friesen says having two hemipenes may benefit males during mating.

“In the