Final answer:
Thomas is comparing the difficulty of recalling memories to the challenge of seeing through muddy water, illustrating the struggle to discern clear images from obscured ones.
Step-by-step explanation:
When Thomas mentions trying to remember as 'looking at an image through a foot of muddy water,' he is using a metaphor to describe the difficulty and lack of clarity in recalling past events. The imagery suggests that his memories are obscured and difficult to discern, similar to the challenge of seeing something clearly through murky, disturbed water. This comparison conveys the frustration and effort involved in trying to recollect something that is not easily accessible or has been muddied by time or other factors. Such a description effectively captures the struggle of peering into the depths of one's memory when it is clouded or obscured by various 'contaminants' of the mind.