Final answer:
A valid paraphrase of an excerpt from "The Odyssey" should capture the central idea concerning the themes, characters, and narrative structure, and avoid merely summarizing plot events without analysis.
Step-by-step explanation:
When paraphrasing an excerpt from "The Odyssey", it is critical to include the central idea that is supported by a textual analysis. In this case, the central idea revolves around the themes, characters, and the narrative structure of the text itself. One should avoid the 'heresy of paraphrase' by ensuring that the structure and form of the original text are considered in conjunction with the content being paraphrased. This means looking beyond just a summary of events and diving into what those events signify in the larger context of the work's themes and the author’s intended message.