According to Osho, the serpent perfectly mirrors Kundalini: it slithers like the first inner surge; moves without legs as pure energy; rests coiled at the base and uncoils upward; forms a completing circle (ouroboros); spreads its hood at sahasrar; can stand on sheer intent; and is innocent yet potent, symbolizing wisdom, alertness, and the danger of wrong stirring.
We use a snake to describe Kundalini because it feels and behaves like one—coiled when asleep, sliding up when awake, opening wide at the top, powerful, wise, and needing careful handling.