Futakuchi - onna

"A futakuchi-onna (二口女?, lit. "two-mouthed woman") is a type of yōkai or Japanese monster. They are characterized by their two mouths – a normal one located on her face and second one on the back of the head beneath the hair. There, the woman's skull splits apart, forming lips, teeth and a tongue, creating an entirely functional second mouth."

- Wikipedia.

I've never known that something like this existed until I saw it as a suggestion in a contest. xD Hahaha. Oh well. 

*Should this be in macabre & horror?