The leg on the bottom acts like a sew-saw of sorts. It pushes down on the ground to lift one leg into the air, then the leg in the air moves forwards or backwards and the leg on the ground moves in the opposite direction. Then the bottom leg pushes on the ground the other way, raising the other leg into the air, after which the elevated leg moves forward/backward and the leg opposite to it moves in the opposite direction. Then the process repeats...
Or at least thats what the robot seems to be doing.
