Did I mention closer examination? Oooh, look at all the little caustics. In this zoomed view, you can see that light is bouncing off the big mirror, hitting the mirrored balls and then landing on the other surfaces. This isn't just caustics - we've got physics going on here. There is one odd thing happening. The big ball has what looks like a blurry reflection of the light-source-surface. But the ball material has no reflective properties (you can't see any other reflections in it) and blurry reflections is not set in the render options. Shrug. Other weird stuff happens in the True Ambience universe, as we'll see in a bit.