It's kinda unnerving, that stare the narcissist gets. It reminds me of the movies of Dracula....that very intense stare meant to unnerve you. It's a look of intense evil....and focused on you like a laser beam.
Done by a man during the love bombing phase, some women initially see this as sexual and seductive, but later, when it's used when the narcissist is angry, it can create fear, and in fact, it's meant to ...intimidate, and it does the job, since it's coupled with a complete lack of empathy or remorse, and an obvious ugliness. It FEELS like what it is....you're being intensely focused on by a totally amoral person. This reptilian stare makes you very uncomfortable, and that's the intent, and it's often coupled with the silent treatment.
This reptilian look in unsettling because it has a predatory aspect, and it often happens rather suddenly, when you disagree or are not sufficiently worshipful of the N's awesomeness. It's an aspect of narcissistic rage, but instead of outrageous anger, it's like watching a fuse on a bomb. It's intense, hypnotic, and makes your blood run cold.
Perhaps you've experienced this, perhaps not. I find it as unnerving as that contorted look of pure evil you see when the mask completely drops. This is another way that the narcissist may appear without the mask.