I don't know much about either animal, stories are that an Ostrich will bury it's head in sand, (don't know if that's true), I think Ostrich's like snake, and they do have those quick feet, but the Anaconda is no slouch either. I think the claws on the Ostrich's feet are pretty strong for digging around rocks and holes in the hardpan soils, so a very minute edge to the Ostrich I think, but it is going to be a tough fight and winner may be maimed for life.