Stick Imitating Larva

This has to be one of the most bizarre larvae I have seen in a long time. It is about 5 cm long and remarkably like a stick in both color and texture, even including some moss. It attaches to a branch by the hind prolegs and protrudes stiffly outwards just like a small twig. The head end is blunt and square with some odd thoracic structures. The true head is very small, dark, almost invisible and is directly above the thoracic legs, which are tiny and held out of sight against the body. It let me photograph it for a while and then suddenly startled me by curling up and springing off into the bush. This is a larva of the Family Geometridae or Loopers, with no middle prolegs.