Imagery in literary nonfiction refers to
description that appeals to the five senses
the author’s attitude toward the subject
the overall presence of a personality behind the text
nonfiction that uses elements and devices common in fictional stories

Imagery in literary nonfiction refers to description that appeals to the five senses. Usually the technique involves using vivid and descriptive language to make the people imagine whatever the author is trying to convey.

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The prompt is "major characters in novels or plays often encounter moral, physical or psychological dangers or choices.  The ways in which the characters respond to these situations frequently reveal the authors' meaning. Analyze how the dangers or choices characters have to make are used by authors to develop their themes."  I doubt that it can be applied to Animal Farm exactly. At least you will get the idea how the author chose the characters. As the back-up, you may turn for the help to the guys I personally know. Check PrimeWritings site for more details.