Brilliant spots of light are streaking wildly around the inside of the plane, like ball lightning, but - and this is far from obvious at first - they are actually projected against the wall of the plane, like flashlight beams. He back-traces the beams, taking advantage of a light haze of vaporized hydraulic fluid that has begun to accumulate in the air, and finds that they originate in a series of small circular holes that some asshole has punched through the skin of the plane while he was sleeping. The sun is shining through these holes, always in the same direction of course; but the plane is going every which way.