id	keyword
hindsight-3591	flame
hindsight-3591	eye
hindsight-3591	eyelid
hindsight-3591	beams
hindsight-3591	visual
hindsight-3591	light
hindsight-3591	optical
hindsight-3591	paper
hindsight-3591	optometry
hindsight-3591	history
hindsight-3591	head
hindsight-3591	years
hindsight-3591	book
hindsight-3591	william
hindsight-3591	rays
hindsight-3591	optics
hindsight-3591	society
hindsight-3591	vision
hindsight-3591	explanation