By day, rokurokubi appear to be ordinary women. By night, however, their bodies sleep while their necks stretch to incredible lengths and roam around freely. Sometimes their heads attack small animals; sometime they lick up lamp oil with their long tongues; and sometimes they just cause mischief by scaring nearby people.
Unlike most yōkai which are born as monsters, rokurokubi and their close relatives nukekubi are former humans—transformed by a curse resulting from some evil or misdeed. Perhaps they sinned against the gods or nature, or perhaps they were unfaithful to their husbands. In many cases, their husbands or fathers actually committed the sin. By some cruel twist of fate the men escape punishment and the women receive the curse instead. In any case, the rokurokubi curse only affects women.
A lord noticed that the oil in his lamps was vanishing at an alarming rate, and suspected one of his servant girls might be a rokurokubi. He decided to spy upon the girl. After she had fallen asleep, he crept into her room and watched over her. Soon he noticed vapors and ectoplasm forming around her chest and neck. A little while later, the servant girl rolled over in her sleep, however only her body moved! The head stayed in its place, and the neck lay stretched out between the two. The next day he fired her. She was fired from every place at which she subsequently worked. The poor girl never understood why she had such back luck with her employment. She never found out that she was a rokurokubi.