Is a living being a poor choice for a Horcrux?

Question

In Harry Potter and the Deathly Hallows, near the end:

Harry allows Voldemort to kill him and learns from Dumbledore that he was a Horcrux (or was acting as one) even though Voldemort had not intended to make Harry a Horcrux. Harry had to die for that part of Voldemort's soul to be released so Voldemort could ultimately die.

From this, we know if a living being is a Horcrux, then when that being dies, the part of the soul associated with that Horcrux is released. Is this always the case?

We also know:

that Nagini is a Horcrux and, unlike with Harry, Voldemort intentionally used Nagini as a Horcrux.

Isn't this a poor choice for a Horcrux, especially considering this being will be in combat, which will make it vulnerable?

It's clear that:

Nagini no longer serves as a Horcrux after she is killed, since Voldemort is able to be killed, which shows us all the Horcruxes have been destroyed.

Is this choice due to arrogance (maybe Voldemort felt this Horcrux would never lose in battle)? Is it likely Voldemort had attempted to make some kind of preparation in case of the Horcrux's death? (Maybe to make sure the body remains as a Horcrux until something else can be done?)

Answer 1

WARNING: THIS ENTIRE ANSWER IS A MAJOR SPOILER FOR HP7! DO NOT READ if you haven't read "HP and the Deathly Hallows" yet!

TL;DR: First, "2 out of 2 cases" were both destroyed in ways that would have destroyed inanimate Horcruxes as well (Basilisc-venom-imbued Sword, and Voldemort's own A.K.); second, even if the destruction was possible via ordinary death, the risk may have been outweighed by benefits for Voldemort as far as Nagini.

2 points in detail:

• Most importantly, Nagini was one of 6 intended ones. So even if you are willing to grant some extra risks, it was a localized risk. So, even if there were downsides to choosing a living thing, they were NOT that big of a deal for Voldemort, given the three benefits:

  • It led to diversification, which seems to have been a strategy for Voldemort as far as safeguarding Horcruxes.

  • Having his snake familiar as a Horcrux may have likely had special significance for Voldemort due to his claim to be the Heir of Slytherin.

  • Related to the last bullet - he needed the last 6th Horcrux "ASAP" (since he was dis-corporated before creating one), and as noted by Dumbledore, he only used items of great significance to house pieces of his soul. There probably weren't many of those around Albania (since the Diadem was already used), and the snake was the only acceptable one as per the last bullet point.

• As Izkata mentions in the comment, it is possible that Nagini may have NOT been un-Horcruxcified except by the same means as destroying inanimate Horcruxes.

  This could have been due to 2 possibilities:

  • Either she was not susceptible to any damage except for the same kind that could destroy Horcruxes. There is not much direct support for this position that I can find, but we know that inanimate Horcruxes were not destructible by normal means (see diary in CoS, or Kreacher's attempts to destroy the locket).

    I don't think this is explicitly proven or dis-proven in the books. Wikia states:

    Concerning Nagini, it is not known if she had to have been killed by Godric Gryffindor's Sword or if any other means, such as a regular sword killing her, would have destroyed the Horcrux.

  • Even if this theory is incorrect when applied to living beings, it's plausible that, had she been killable with the conventional weapon, the body may have remained a Horcrux. There is nothing to indicate in any way that the V's soul fragment was in any way tethered to the "alive" part of the snake.

Answer 2

Yes, turning a living being into a Horcrux is a terrible idea.

At least according to Dumbledore, that is:

“The snake?” said Harry, startled. “You can use animals as Horcruxes?”
“Well, it is inadvisable to do so,” said Dumbledore, “because to confide a part of your soul to something that can think and move for itself is obviously a very risky business. However, if my calculations are correct, Voldemort was still at least one Horcrux short of his goal of six when he entered your parents’ house with the intention of killing you...
...After an interval of some years, however, he used Nagini to kill an old Muggle man, and it might then have occurred to him to turn her into his last Horcrux. She underlines the Slytherin connection, which enhances Lord Voldemort’s mystique; I think he is perhaps as fond of her as he can be of anything; he certainly likes to keep her close, and he seems to have an unusual amount of control over her, even for a Parselmouth.”
_{(Half-Blood Prince, Chapter 23, Horcruxes).}

There are several reasons why creating a living Horcrux is not a smart thing to do.

• That being could theoretically betray you or commit suicide in order to render you mortal again. Having your soul inside them may give you a certain amount of leverage and control but that control is not total. Harry Potter is evidence enough of that.
• The being could die in a freak accident, just like any other being. It could fall off a cliff or be caught in a fire at any given moment.
• Living beings move about, which makes them easier to track and identify for any enemies who are hunting your Horcruxes.
• Possessed creatures act strangely and have certain give-away behaviours (like Harry's visions) which betray that they're being used as Horcruxes. This, again, makes them vulnerable to attack.

The whole rationale of having a Horcrux is that it's supposed to be totally secret and totally secure. There's not really much point in having it if somebody that wants you dead can track it and destroy it. By placing a portion of your soul in a living, breathing animal or person you are effectively entrusting your soul to chance. Because they are moving around freely disaster could strike them at any moment. You are also dangling them in front of your enemies, making it more likely that they might destroy your Horcrux.

Consider the times when Nagini was in danger. She was around in the graveyard during Voldemort's rebirth; Harry could have killed her, either intentionally or by accident. She went on a solo mission to the Ministry of Magic, where she could easily have been attacked by Arthur Weasley (if he'd been conscious) or another Ministry wizard. She acted as bait for Harry and Hermione and could have been killed in that fight. And, of course, she attended the Battle of Hogwarts, when she was killed out-of-the-blue by Neville Longbottom, someone that Voldemort would never have seen as a threat to his Horcrux. Nagini may have been able to look after herself, generally speaking, but she was still vulnerable to attack.

Looking again at Dumbledore's quote, it seems clear to me that Voldemort was well aware of the risks and downsides to using Nagini as a Horcrux. However, he was one Horcrux short at the time and he used Nagini partly out of desperation. His affection for her may have blinded him somewhat. Using her was still a bad idea, as her death ultimately demonstrated.