self-shading is a problem common to ray-tracing engines where the math, due to minor imperfections, results in an item shading itself incorrectly. Imagine a floor that has "cast shadow" turned on. Now imagine that the shadow it casts falls on itself... Most render engines that I know of have a "bias" setting of some sort that allow you to add or subtract a variable amount to the "at surface" to start casting the shadow at. So the shadow falls BELOW the object by x amount not actauuly ON the object. Cheers, Cliff