Second Variety by Philip K. Dick.
Those of you who have read the story Second Variety (first published in the May 1953 issue of Space Science Fiction magazine; the story is available online here) will appreciate this clip about new robots being built for the US Army that remarkably mimic biodynamics.
Have a look at the eerie and impressive movements of this quadrupedal pack robot, made by Boston Dynamics. This is an updated video from March 2010.
Big Dog Robot, Boston Dynamics.