What type of damage does Avada Kedavra do?

Question

Avada Kedavra kills things, that much is known, but what kind of damage does it actually do? Does it just stop all bodily functions? Does it force the soul to pass on? Damage the soul? Has J.K. Rowling actually explained the way it works in any way?

One thing does point to the bodily death only, as apparently Fawkes, an immortal phoenix, could swallow the spell and be reborn with no harm (apparently) to its soul.

Fawkes swooped down in front of Dumbledore, opened his beak wide, and swallowed the jet of green light whole. He burst into flame and fell to the floor, small, wrinkled, and flightless. […]

The hall was quite empty but for themselves, the sobbing Bellatrix still trapped under her statue, and the tiny baby Fawkes croaking feebly on the floor— […]

He did not look at Harry at first, but walked over to the perch be- side the door and withdrew, from an inside pocket of his robes, the tiny, ugly, featherless Fawkes, whom he placed gently on the tray of soft ashes beneath the golden post where the full-grown Fawkes usu- ally stood.

— Order of the Phoenix, chapters 36 and 37

But could that also mean if you can get the heart pumping again the person could be restored? Or is it more of a "irreparable magical damage to the body" thing?

(Do note this is asked mostly from the point of view of crossover battle speculation, i.e. would immortals of another verse with no magical resistance be impervious to Avada or not.)

Answer 1

Does it just stop all bodily functions? Does it force the soul to pass on? Damage the soul? Has J.K. Rowling actually explained the way it works in any way?

There's no explicit explanation, but from several pieces of info we know that:

• It separates the soul from the body with no physical damage to the body (ref: DH, discussion about the death that Muggles couldn't explain but was AK)

  • In the special case of AK that rebounded on Voldemort from Lily's love protection magic, it blasted Voldemort's soul piece from his soul.

    This was explained by Dumbledore as a consequence of the fact that the soul was unstable due to multiple Horcrux-creation splitting before, and thefore shouldn't be the case in normal deaths by AK (DH, as well as GoF Riddle murders). But as usual for this answer, there's no definitive canon proof that's the case

• The body dies; and at the very least, there's no muggle-visible damage or cause of death at all

  It's unknown if what kills the body is the effect of the curse OR simply the fact that the soul was separated.

  However @Legion brought up a good point in comments - Dementor's kiss separates your soul without killing the body. So it's likely the physical death is the effect of AK itself.

One thing does point to the bodily death only, as apparently Fawkes, an immortal phoenix, could swallow the spell and be reborn with no harm (apparently) to it's soul.

Unconfirmed. We don't know from canon whether phoenixes even have souls. Or if there's something special about their bodies AND souls that enables rebirth.

But could that also mean if you can get the heart pumping again the person could be restored? Or is it more of a "irreparable magical damage to the body" -thing?

The soul is fully separated, and as far as I'm aware, there's no canon support for the soul being able to reconnect back to the body past that separation. But there's really no support to disprove that possibility either, as far as I can tell.

Answer 2

The books never say one way or the other how the spell actually operates. Likewise, it doesn't explain why holding a stick, waving it, and yelling "Wingardium Leviosa!" will make an object float. There will always be a degree of uncertainty regarding the actual theory behind spells.

That said, my guess is that the spell operates primarily by ceasing all bodily functions.

There is already a manner of soul removal in the Harry Potter series: the Dementor's Kiss. Those who receive the Kiss have their souls removed, but their bodies stay alive as an empty husk. So at the very least, the Killing Curse must go beyond simply removing the soul.

Also, the spell is shown to be able to kill animals like Hedwig and ordinary spiders. At the risk of starting a flame war with PETA, I doubt those creatures have "souls" like humans and other Beings. I think this would also explain why Fawkes can survive the Killing Curse. Phoenixes can survive bodily death by the immediate creation of new body. But if the spell actually "expelled" or "damaged" Fawkes' "soul," I don't see how he could possible survive it.

The only potentially troubling aspect of this approach is that, as you point out, someone could presumably be revived the way clinically dead people are revived all the time in the Muggle world. But remember, the Killing Curse is considered part of the Dark Arts. Any bodily damage received from a Dark curse cannot be healed, i.e. George's ear and Mad-Eye's various appendages. So even if it only causes bodily damage that would normally be reversible, it would be still be irreversible.

Answer 3

Just a guess, but I think it rips the soul from the body.

In the Harry Potter universe, there’s a clear distinction between bodies and souls, and one can exist without the other – see ghosts, horcruxes or Dementors for examples.

The three deaths we hear about in the opening chapter of Goblet of Fire show no damage to the body, other than they happen to be dead:

The police had never read an odder report. A team of doctors had examined the bodies and had concluded that none of the Riddles had been poisoned, stabbed, shot, strangled, suffocated, or (as far as they could tell) harmed at all. In fact (the report continued, in a tone of unmistakable bewilderment), the Riddles all appeared to be in perfect health — apart from the fact that they were all dead. The doctors did note (as though determined to find something wrong with the bodies) that each of the Riddles had a look of terror upon his or her face — but as the frustrated police said, whoever heard of three people being frightened to death?

— Goblet of Fire, chapter 1 (The Riddle House)

It seems that their souls have left their body, but without damage. Likewise, when Voldemort attacks Harry in the final book, his soul goes to limbo without any apparent damage, while his body lies lifeless in the Forest.

I think a reanimated corpse from Avada Kedavra might be like somebody who’s suffered the Dementor’s Kiss – it is biologically sound, but without a soul. As the Dementor’s Kiss shows us that a body can survive without a soul, perhaps Avada Kedavra does do some physical damage, which is undetectable to Muggle medicine. Or perhaps it just flips a biological “off” switch. But that’s all just speculation.

Unless you can put the soul back into the body, it remains lifeless. But as we see in Deathly Hallows, Harry’s soul returns to his body and it returns to life, apparently undamaged by the experience. So I would guess that Avada Kedavra really does just separate the two, and not permanently damage them.

This is the description of Avada Kedavra given when Moody introduces it in class:

There was a flash of blinding green light and a rushing sound, as though a vast, invisible something was soaring through the air — instantaneously the spider rolled over onto its back, unmarked, but unmistakably dead.

— Goblet of Fire, chapter 14 (The Unforgivable Curses)

In my mind, I’ve always imagined that rushing sound to be the soul leaving the body. But that’s a personal theory – I’m not aware of anything to back that up.

As for the soul itself, I believe Avada Kedavra leaves it undamaged. Harry has been struck with two killing curses, and there’s no evidence of damage to his soul. The brief glimpses of other people killed by Avada Kedavra – Harry’s parents, or Dumbledore – also show no evidence of damage to the soul on the same scale as, say, Voldemort’s horcruxes.

Answer 4

I'd like you to understand, before I say any of this, that death isn't a singular event, but a process. First comes clinical, and then biological death. Clinical death occurs when the heart stops beating and the circulatory and breathing system stops working. Biological death is rather permanent, damage to the circulatory and breathing system which is irreparable, after biological death reviving the dead person is impossible. However, as many have said, it rips the soul from the body. So I'll guess that ripping the soul from the body would stop the circulatory or breathing system, but never cause irreparable damage, maybe it'll cause clinical death, followed by biological death. Or maybe it just skips clinical death and fast forwards all the way to biological death. So you have 3 answers from me.

1. It rips the soul from the body, but doesn't do irreparable damage to the body itself.
2. It causes clinical and then biological death.
3. It skips to biological death...

Also, I have a fourth guess.

4. It rips the soul from the body, but it never causes biological or clinical death, heck, it doesn't do damage to the body for that matter. It just separates body and soul, and afterwards makes it impossible for the soul to return into the body, and makes revival impossible.

Take these four answers and do what you will. This is just a guess so I don't take any of this as fact until confirmed.