In the battle at the Ministry in OotP, why did the Centaur statue break but the Wizard statue didn't?

Question

During the fight between Dumbledore and Voldemort (and Harry and Bellatrix) in the atrium at the Ministry of Magic in chapter 36 of Order of the Phoenix, Dumbledore uses various ploys to dodge, intercept, and otherwise not die from Voldemort’s Avada Kedavras.

Two of those involve animating the statue in the Fountain of Magical Brethren and letting the spells hit animated statues instead of Harry or Dumbledore themselves:

The wizard

‘I have nothing more to say to you, Potter,’ he said quietly. ‘You have irked me too often, for too long. AVADA KEDAVRA!’
    Harry had not even opened his mouth to resist; his mind was blank, his wand pointing uselessly at the floor.
    But the headless golden statue of the wizard in the fountain had sprung alive, leaping from its plinth to land with a crash on the floor between Harry and Voldemort. The spell merely glanced off its chest as the statue flung out its arms to protect Harry.

The centaur

Next second, he had reappeared behind Voldemort and waved his wand towards the remnants of the fountain. The other statues sprang to life […] and the one-armed centaur galloped at Voldemort, who vanished and reappeared beside the pool. The headless statue thrust Harry backwards, away from the fight, as Dumbledore advanced on Voldemort and the golden centaur cantered around them both. […]
    Another jet of green light flew from behind the silver shield. This time it was the one-armed centaur, galloping in front of Dumbledore, that took the blast and shattered into a hundred pieces, but before the fragments had even hit the floor, Dumbledore had drawn back his wand and waved it as though brandishing a whip.
_{Both quotes from Order of the Phoenix, chapter 36: “The Only One He Ever Feared”; emphasis mine}

So both statues get animated, both statues come between Voldemort’s Avada Kedavra spells and their targets—yet the spell glances off one statue and shatters the other into a hundred pieces.

 

Why did the statue of the centaur shatter when hit by the Avada Kedavra spell, when the statue of the wizard didn’t?

Note that the suggested dupe simply asks what Avada Kedavra does to inanimate objects, which evidently varies by what type of object we’re dealing with. This question asks specifically why two supposedly identical (except in shape) parts of the same stone statue/artwork react in different ways to each other right after each other.

Answer 1

From the text, we see that the wizard statue only received a glancing blow:

The spell merely glanced off its chest as the statue flung out its arms to protect Harry.

The majority of the energy from the spell would have bounced off it rather then being absorbed by it. This meant the wizard statue survived its encounter with Avada Kedavra intact. The centaur statue

took the blast and shattered into a hundred pieces

which implies that the spell was a direct hit and therefore received the full impact from the magical energy fired at it. This was enough to shatter the statue of the centaur.

Furthermore, the wizard statue is stated to be "golden", whereas the centaur statue is not. The gold surface of the statue may also have contributed to its survival compared to the statue of the centaur.

Answer 2

It's possible that the second spell that Voldemort cast was not actually Avada Kedavra.

The only description that we get is that Harry sees a green flash. This could possibly be any number of spells, there is almost certainly more than one spell that produces a green flash.

It's unlikely that the killing curse doubles as an exploding statue spell, if I remember correctly it drains the life from a living creature. This means that if the statue exploded, there's a good chance that it was not the spell that Voldemort chose to use.

Considering how accomplished a wizard that Voldemort is, it's possible that he predicted Dumbledore's defense of his curse, as he had used a statue to do the exact same thing only seconds earlier to protect Harry. Therefore, predicting Dumbledore's preemption of the Avada Kedavra spell he decided to send a similar looking disintegration spell instead.

This would mean that If the statue took the hit, then Dumbledore would have one less weapon at his disposal (it had attempted to charge down Voldemort just before). Even if Dumbledore hadn't been able to shield himself in time, it would still have had the potential to cause significant damage.

Answer 3

There are two possible reasons here.

1. Dumbledore's spell enhanced its defense.

Obviously Dumbledore was an extremely talented magical genius, certainly capable of enchanting a statue to withstand this, especially since Avada Kedavra doesn't kill it. Since it was meant to protect Harry, while the centaur was only meant to deflect the spell, it would have been logical for Dumbledore to use the statue in this way.

2. The centaur statue was worse material

The Wizarding world at that time was not exactly centaur-centric. It was focused on wizards, and there were many anti-(insert non-human creature here)s, like Umbridge. I could definitely see the centaur, goblin, and elf being made out of some less sturdy material, for whatever reason (expense, time, shortages, etc.)

Answer 4

I feel that the spell that glanced off the golden statue of the wizard was a less powerful Avada Kedavra as it was intended for Harry. If we remember that spells can have different degrees of strength, you could say it would still have killed Harry if it struck, but in comparison to the spell that he cast at Dumbledore, it was lacking in strength.

To me it shows the ferocity of the duel that he and Dumbledore had, using spells at stronger magnitudes than they would normally use, Voldemort putting more "cause of pain" as Bellatrix puts it.

"Crucio!" Bellatrix screamed: the spell had knocked her off her feet, but she did not writhe and shriek with pain as Neville had - she was already back on her feet, breathless, no longer laughing. Harry dodged behind the golden fountain again. Her counter-spell hit the head of the handsome wizard, which was blown off and landed twenty feet away, gouging long scratches into the wooden floor. "Never used an Unforgivable Curse before, have you, boy?" she yelled. She had abandoned her baby voice now. "You need to mean them, Potter! You need to really want to cause pain... -OoTP