The rokurokubi (ろくろ首, 轆轤首) is a type of Japanese yōkai. There are two types, the ones whose necks stretch, and the ones whose heads come off and fly around freely. They often appear in classical kaidan and essays, and they are often the subject of yōkai depictions, but have also been pointed out that most have been created in order to satisfy Japan's hobbies with supernatural stories.
They always appear not very different from humans. The type whose neck stretch possess a neck that stretch and shorten very long. The origin of the word "rokurokubi" has several theories, including the possibility that it comes from the feeling of making pottery with a rokuro (a potter's wheel), the possibility that an elongated neck resembles a well's rokuro (the pulley for pulling up loads), or the possibility that an umbrella's handle seems to elongate when opening an umbrella's rokuro (the device used to open and close umbrellas), among other theories.