Defense contractor Boston Dynamics has recently posted video of its BigDog four-legged robot pack mule in action. Funded by DARPA, BigDog is being developed for the US military to carry heavy gear for soldiers across terrain that is not suitable for vehicles. Measuring a little over 3 feet long by 2.5 feet high and weighing 165 pounds, it is indeed closer in size to a large canine than a pack mule. Nonetheless, BigDog seems up to the challenge. It can walk at speeds of up to 3.3 mph, climb 35 degree slopes and carry loads of 120 lbs, following a simple path autonomously or more complicated routes under remote control.