The wielding animation of the undead chicken was updated in June 2009 to be a smoother version of the "idle" animation before the huge graphical overhaul. However, for a long time after the release of RuneScape HD, the graphical animations of a player while wielding an undead chicken were not updated along with the rest of the wieldable weapons.
Both the old and new animations for the undead chicken made players turn their head to the right every so often.
As of the Evolution of Combat, the undead chicken is one of several weapons which will cause the player character to have the old idle and running animations when equipped. While in Legacy Combat mode, the player will have the old idle animations, however, not while using EoC.