I asked a question here, in which @Scanner pointed out that there was a fundamental part of the question that was missing.
How does a Basilisk kill with its eyes? Does it sever the soul, cause instant brain melting, cause spontaneous combustion, or is there some other mechanism at work?
In Fantastic Beasts and Where to Find Them, it’s stated that looking directly into a basilisk’s eyes causes instant death. However, it’s not said how looking into the basilisk’s eyes kills.
“It has exceptionally venomous fangs but its most dangerous means of attack is the gaze of its large yellow eyes. Anyone looking directly into these will suffer instant death.”
- Fantastic Beasts and Where to Find Them
When Myrtle describes how she died, she said she saw yellow eyes, seized up, and then was floating away (so she was dead right after seizing up). It was very quick.
“So I unlocked the door, to tell him to go and use his own toilet, and then –’ Myrtle swelled importantly, her face shining, ‘I died.’
‘How?’ said Harry.
‘No idea,’ said Myrtle in hushed tones. ‘I just remember seeing a pair of great big yellow eyes. My whole body sort of seized up, and then I was floating away …’ She looked dreamily at Harry. ‘And then I came back again.”
- Harry Potter and the Chamber of Secrets, Chapter 16 (The Chamber of Secrets)
We don’t know what her body looked like, so we don’t know what damage looking into the basilisk’s eyes caused but ‘seizing up’ almost sounds like she’d been something like Petrified, but in a strong enough way to actually kill. This would fit with how people who see its eyes indirectly get Petrified but not killed, but there’s no confirmation that this actually is how it works.
Impossible to answer from canon as far as I know. Moaning Myrtle's account certainly sounds like it is an instant effect.
However it is clearly not a spell in the way that Avada Kedavra is. (or we'd see green flashes flying out of its eyes constantly) I think it is something triggered in the victim when eye contact is made. A more subtle kind of magic perhaps. It seems like the brain decides to shut itself down at source.
It is probably trivially easy to stop being alive, we have just evolved to avoid doing so. The Basilisk's eyes could be compelling the brain to commit suicide while unlocking the, generally avoided, ability to do so. This has the bonus of being much more sinister than a generic killing spell, for me at least, as it uses the victim's own body against them.
The basilisk DOES kill by eye-to-eye contact. All the petrified victims don't meet the basilisk's gaze.
According to Greek mythology, the basilisk never had the power to petrify. There are no known accounts of someone looking at a basilisk's eyes indirectly in reflection or in any other way.
What the petrification reminds me of is Medusa. It seems Rowling incorporated that old legend into the Harry Potter saga.
Of course, doesn't really explain HOW the petrification worked. Maybe petrification is a watered down version of death? It can also be conjectured that petrification is a state which is closest to the state of being dead, without actually being dead.
Maybe the power would've been diluted even more if more reflections of the basilisk's eyes were involved.
EDIT: TO THE ACTUAL QUESTION.
From the book, we see that Mrs. Norris is petrified. In the Harry Potter universe, I don't really recall the souls of animals being present. Except horses? The Ghosts of Hogwarts? Supposing that animals DID NOT have souls, the severing the souls concept doesn't hold up.
Using purely my imagination here, a basilisk's eyes COULD vaporise the chi of a living being. The life force of a living being that is.
According to legend though, the only way to kill a basilisk is to make it look at its own reflection. It would then die of fright. From this, we COULD conjecture that its victim dies of fright. This doesn't reeaally gel with the petrification power though.
I'm always amused and intrigued when an author leaves important details (such as the functioning of devices, objects, etc) up to each reader's minds as though it's subjective enough for everyone to be right. Sometimes they just don't care to bother, which is more frustrating when that author has gone to great lengths to create details for so many other items in their stories.
Having said that, I think occam's razor might best provide the answer to the question. Of course all attempts to answer this question is pure supposition or conjecture. There's a passage in the book which states that all those who meet the beam from its deadly eyes will die from this murderous glare. Apply occam's razor to that and maybe we're actually talking about a beam shot or from the eyes of the basilisk. It could be a steady stream always on our the basilisk could even possibly control when beams actually shoot out from the eyes. The beam itself, could be invisible as Moaning Myrtle described seeing a pair of yellow eyes but not an actual beam (something akin to a laser or something). The explanation for the petrified victims also fits as this "beam" could get weaker with distance AND/OR reflection! Since none of the victims, during Harry Potter's era, were directly exposed to this beam they were only petrified.
As for the actual mechanical, physical or literal process of why the beam actually kills..... There are a few explanations "each as unlikely as the next"... But I think that a full dose of the beam would fry the brain causing instant damage and death.... But a weaken dose only temporarily disables motor function causing paralysis or permanently damages the brain thus disabling motor function & paralysis. In either case, the damage done is curable via a potion concocted from parts of stewed mandrake remains amongst other ingredients. I think the "beam" explanation is a more likely scenario of all those that might exist. It's easy to just throw out the term "it's magic" but even "magic" has to have a process by which it works including limitations reducing or even nullifying effects.
Thoughts?
I think i figured out how it works both Basilisk Stare in eye works, Harry Potter Ghosts and bit of soul parts etc. I am going to give you 4 Reasons/Clues first.
Clue/Reason 1
1 The basilisk stare turns you to stone when you catches its eye in a reflection, glass/water etc... the petrified student does not need to do the things you do everyday I am talking of things like eating, going to toilet sleeping, Socialising. But people does not 'forget' you exist or anything or existed but you are in essence like dead to the world.
Clue/Reason 2
It kills when its eyes meets its target now why is that? one guy talked about a 'beam' and that its always on but I am quite sure thats not how it work but i believe the guy was not completly wrong I think he is in the right direction is a sense.
Clue/Reason 3
As everyone probably knows/heard of this And yes I am taking a quote not from HP here: The eyes are called 'the window of the soul' -William Shakespeare. So the 'soul' is basically The 'core' of who you are, and it is said that the soul can be seen through the eyes.
Clue/Reason 4 and last. If we look at the ghosts of Hogwarts specifically ghost Nick he got turned to stone it was no different really compared to the 'living', the basilisk stare in a sense even sort of harms the soul it simply must be like that, there is no other alternative. HP quote: What could possibly even harm the dead?
With these 4 Clues etc I will now form a hypothesis consistent with several parts I believe is true to each part of how the gaze works etc.
Hypothesis part 1 So what if its true gaze is actually not severing the soul or making someone want to suicide etc? But does instead freeze/petrify the soul? A frozen soul in a body would it not mean the body would shut down in a sense? Could it not act as if it was severed? If so then it would to the body be as if the soul no longer exists in it since it can't sense the soul.
Hypothesis part 2 Now how long would/could the soul or a ghost stay frozen? Well a ghost in my theory is a spiritual construct that is sort of a clone of who the real person was in life but possibly with a link to the soul in afterlife. So probably as long as the magic is around id say/believe.
Hypothesis part 3 In a body the Soul probably would not stay frozen/petrified for long in a body I believe because it would be ejected eventually and the magic would break, the body is said to be merely a container after all and the basilisk stare hits the eye first thus magic should be centered there if you will. Thus the magic is most likely circling or so in the body and once the soul gets ejected the magic stays in the body not following the soul. And when it is about to hit the soul through a 2 reflection like Mirror/water then to the eye, the effect is simply cast upon the body instead Exactly why is something of a 'mystery' but a Hypothesis here is coming
Hypothesis part 4 what if to the magic of the basilisk gaze, 'the eye' of a person/being/ghost is also magically ruled as a reflection to the soul? And if we take that into consideration since the mirror/water reflection was 1 what if the gaze is simply not reaching the soul and instead the magic gaze affects only and on the body instead of the soul? This would make the body not dead, but like frozen in a sense the soul is still linked-up/tied to the body and therefore the person does not die.
I think that the Basilisk was based on Medusa, so it's a possibility that the eyes of a Basilisk send a ray that turns the organs into stone.
In my point of view, I suggest that the Basilisk’s sending a piece of its soul, which could be poisonous in nature or a human can not handle it in anyway, into a human through eye contact. Like how most witches and wizards use a wand to direct their magic, a Basilisk uses its eyes.
Or, it could be a swap in certain extremely small and resilient DNA strands that instantly make our own cells decay and rot which leads to us dying instant.
It honestly depends on opinion and what J.K Rowling tells us.
