Originally developed for spying activities, this technique can be done after some surgery and actual body modification. The user dislocates their joints then controls their softened body with chakra, allowing them to stretch and twist any part of their body at any angle, elongating and even coiling around their opponent. This can also be used to make the user's body more malleable and snakelike. Orochimaru's version allows him to stretch any of his body parts well beyond their normal length and allows him to move in the manner of a snake.
This technique is based on yet another aspect of Japanese folklore. Rokurokubi (ろくろ首) are yokai (Japanese spirits or demons) that were originally humans, but broke the precepts or doctrines of Buddhism. Cursed, these monsters had infinitely extendable necks and used them to spy on mortals. The worst of these preyed on humans or bit them and drank their blood (much like how Orochimaru gives his cursed seals).