What effect did the author most likely intend with the description “Behind them the line of woods gaped like a dark open mouth”?(Paragraph 79)

The author describes the woods as “a dark open mouth" to foreshadow the way the family will meet their deaths and also suggestive of how the story will end.

Explanation:

Flannery O'Connor's short story "A Good Man is Hard to Find" revolves around the story of a family's road trip that will lead to their deaths. And the tragic fate was a result of the grandmother's insistence that they go sightseeing, which led them to their car accident and discovery by prison escapee "The Misfit".

In describing the woods where they were stuck in as a "line of woods [that] gaped like a dark open mouth”, the author provides a foreboding of how the family will meet their fates. He personifies the woods as 'opening its mouth' and waiting to devour the family, suggestive of the imminent death of the whole family at the hands of The Misfit.

This description was the author's intention of predicting or foreshadowing the killings of the family members by The Misfit.  

jim mohr

explanation:

"the sandy walls seemed to collapse in on themselves"

and

"the bloodshot waters seemed to have no bottom"