I'm not sure if the "no metaphors" was meant literally, or more to say, "no cheap outs, actually describe what you are seeing." Even some technical terms, as you note, were originally metaphorical, or just descriptive in Latin or Greek. (Example: "phylloid" simply meaning "leaf shaped.") Somethings can only be described metaphorically, such as sounds. I'm going to go out on a limb (ouch! that was not deliberate) and assume he also meant "no easy cliches for description." Also, how about assumptions? Why were you assuming why Carrie was barking? You're probably right, but it is an after-the-fact thought process, not an immediate description.
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