In Japanese folklore, rokurokubi are yokai that appear as regular women but with the curious ability to extend their necks. There are actually two types of rokurokubi, one whose neck is able to stretch out to an extraordinary length and wander around while the body is sleeping. The other is known as nukekubi, and in this case the head can actually detach from the body and fly around freely. 

Backemono no e, ca. 1700

These strange extended and wandering heads have been known to lick the lamp oil at night, attack small animals and basically scare people senseless. It is believed that rokurokubi were once human but transformed into yokai as a result of some form of curse. In some cases it is even said that the rokurokubi results from the sins of a male family member, but the woman bears the punishment by receiving the curse. Considering the injustice of this, it's no wonder she wants to scare people.

Shigeru Mizuki

There are many legends and tales of rokurokubi in Japanese folklore and varying origin theories. If you want to read one interesting tale about rokurokubi, yokai expert Matthew Meyer has written more on his website.

Katsushika Hokusai
Toriyama Sekien