Sentence:  Here in the cool darkness Mr. Podger could still feel the warmth of midday , could still see the yellow butterflies dancing over the road , could still see the friendly grin on the young , sun-browned face as the driver <WSD>looked</WSD> back over his shoulder for a moment before the car streaked out of sight . 
Meaning of the word marked with <WSD> tags:  look towards one's back