The Deer-Leg, or Venison, is the stifle and hock of a young Deer. It appears quite common in the time of The Dark Project, but its popularity has dwindled in recent years becoming a rarity during The Metal Age and completely absent from Thief: Deadly Shadows (perhaps due to the increasing mechanization of society, expansion of urban civilization, and active carnage that the Mechanists wrought against nature in the previous titles).
Like all food items, it has a chance of restoring one point of health in Thief II: The Metal Age.