Not a cloud in the sky. Sitting on south-facing deck, enjoying beautiful autumn weather. I'm retired, so I do this often, day and night. No other aircraft in sky at this time, neither general, commercial, or military. University of Oklahoma's national weather service launches weather balloons, which I have seen often and mostly appear motionless except for the instrument packages dangling wildly beneath on their tether. This was nothing of the sort.At upper left limit of vision, noticed something traveling at a very high rate of speed. Immediately recognized it as something far beyond the "norm', and immediately rose from my chair, moved to south edge of deck, realizing that it would quickly leave my observation when it passed beyond my roof top.Its heading was very near 360, and its path was approximately above I-35, which is about 3/4 mile to my east. Its altitude, a guess, was about 2,000 to 3000 feet. Its speed, a guess, was at least 600 knots, or traversing the sky at least triple the rate of commercial airliners as they level out into landing patterns for OKC. Shape appeared spherical ... color and texture was similar to a cloud. So, I saw a small cloud, maybe 40' in diameter, traveling near the speed of sound ... making no sound. Before it passed from view, it made 2 very quick "zig-zags", moving right and then immediately forward, in less time than it takes to quickly say "zig-zag" twice. It then continued on its 360 heading.