Rokurokubi
Rokurokubi (轆轤首) is a Japanese yōkai that looks like an ordinary person, usually a woman, by day but whose neck stretches to surprising length at night, letting her head roam, spy, and lick lamp oil. Folklore warns that a person whose neck aches at night may be a rokurokubi; the head can be kept from rejoining the body if the neck or torso is hidden or blocked.