Penis Mouse

The Penis Mouse is a mouse with a penis growing on its back that made its only appearance in the Season Twelve episode "Eek, A Penis!"

Background
When Ms. Garrison regrets having a sex change operation, she goes to a research group asking them if they can grow a penis on a mouse's back after seeing a mouse with an ear growing a its back. Later on, they have shown to have successfully grown a penis on a mouse, but when Ms. Garrison tries to hold it in her hand, she accidentally lets the mouse loose. She and the researchers run around town trying to capture the mouse to no avail. The mouse however, eventually finds Ms. Garrison sitting on a bench and gets into her hand. Later, at South Park Elementary, Ms. Garrison is shown to have underwent her surgery to become a man again and seems to have kept the mouse as a pet, though it hasn't been seen in any future episodes.

Appearance
The mouse appears as a typical mouse with white fur, red eyes, a pink nose, pink paws, and a long pink tail. It has a large penis growing on its back, which is removed after Ms. Garrison's sex change. The mouse and penis are capable of speaking independently of each other with high pitched voices.