Venus the Two-Faced Cat a Mystery}

Venus the two-faced cat is currently the most famous feline on the planet.

The three-year-old tortoiseshell has her own Facebook page and a YouTube video that's been viewed over a million times, and appeared on the Today Show last week. (Watch National Geographic cat videos.)

One look at this cat and you can understand why: One half is solid black with a green eye—the other half has typical orange tabby stripes and a blue eye.

How does a cat end up looking like that? Leslie Lyons, a professor at the University of California, Davis, who studies the genetics of domestic cats said she's never seen a cat exactly like Venus.

"She is extremely, extremely rare," Lyons said. "But you can explain it and you can understand it."