In earlier periods of Human History, the Serpentine Unicorn was classified as a dinosaur. Now we know better, and the Serpentine Unicorn is officially classified as a member of the Unicorn species.
The Serpentine Unicorn is a much darker being than it's mammalian counterpart. The forked tongue and glowing eyes offer no evolutionary benefit, but instead make the being more intimidating to those capable of differenciating between good and evil. The Serpentine Unicorn can and will hurt you, and your loved ones using a special kind of photographic memory, in which it steals your photo album and tracks down everyone in it.
George: "Did you see that Unicorn?"
Bill: "I believe it was a Serpentine Unicorn."
Bill: "Because my left arm and leg are now missing."