Claim. The Genesis-3 serpent is a symbol for a spiritual being — specifically an angel originally created with good purpose who later fell and became Satan. It is not a literal animal.
Elaboration. Per 1.2. The Identity of the Serpent: the serpent could converse with people, knew God’s Will (the prohibition), and was identified in 9 with “the great dragon… that ancient serpent, who is called the Devil and Satan, the deceiver of the whole world.” Since the entity called Satan is a spiritual being that “lived in heaven before it was thrown down,” the serpent must symbolize a spiritual being too.
What kind of spiritual being could converse with people, know God’s Will, live in heaven, and after falling dominate the human soul across time and space? “There are no beings endowed with such characteristics other than angels.” 4 (“God did not spare the angels when they sinned”) confirms the conclusion.
The serpent-image itself encodes the angel’s character: “A serpent has a forked tongue. It depicts someone who utters contradictory things with one tongue and lives a two-faced life with one heart. A serpent twists its body around its prey before devouring it, a metaphor for someone who ensnares others for his own benefit.”
DP also rules out a pre-creation evil principle: if the seducing spirit existed before creation with a purpose contrary to God’s, monotheism collapses and the providence of restoration would be futile. The seducer must be a created archangel who fell.