Why did Malfoy's Petrificus Totalus work on Harry while he was wearing the Invisibility Cloak?

Question

In Harry Potter and the Half-Blood Prince, after Harry eavesdropped on Malfoy on the Hogwarts Express, Malfoy cast Petrificus Totalus on Harry while Harry was wearing his Invisibility Cloak.

How did the spell work, when Deathly Hallows tells us that no spell used against the Invisibility Cloak will work? (Harry's cloak was not an ordinary cloak and was a gift by Death, himself, to his ancestors, passed down to him)

To prove my point, sometime later in Deathly Hallows, one of the Death Eaters tried to Accio the cloak to find Harry, which didn't work.

So this contradicts J.K. Rowling theory.

Ah, but the Third Hallows is true Cloak of Invisibility, Miss Granger! I mean to say, it is not a traveling cloak imbued with a Disillusionment Charm, or carrying a Bedazzling Hex or else woven from Demiguise hair, which will hide one initially but fade with the years until it turns opaque. We are talking about a cloak that really and truly renders the wearer completely invisible, and endures eternally, giving constant and impenetrable concealment, no matter what spells are cast at it. How many cloaks have you ever seen like that, Miss Granger?

Answer 1

While in Deathly Hallows, Xenophilius Lovegood describes the Hallows cloak as being inpenetrable in all ways; J.K. Rowling contradicts this in Tales of Beedle the Bard:

True Invisibility Cloaks, though rare, exist in this world of ours; however, the story makes it clear that Death’s Cloak is of a uniquely durable nature.

_{Tales of Beedle the Bard - Page 96 - Bloomsbury - *The Tale of the Three Brothers}

Invisibility Cloaks are not, generally, infallible. They may rip or grow opaque with age, of the charms placed upon them may wear off, or be countered by charms of revealment. This is why witches and wizards usually turn, in the first instance, to Disillusionment Charms for self-camouflage or concealment. Albus Dumbledore was known to be able to perform a Disillusionment Charm so powerful as to render himself invisible without the need for a Cloak. [JKR]

_{Tales of Beedle the Bard - page 97 - Bloomsbury - The Tale of the Three Brothers}

So, Death's cloak is thought to have been of a uniquely durable nature, which I take to mean stronger and perhaps more magical than, say, an Invisibility Cloak woven from Demiguise hair by the witch next door who likes knitting as a hobby. J.K. Rowling goes on to say that Invisibility Cloaks are not infallible -- generally. Yet Harry's cloak demonstrates it is not infallible on a few occasions. Quite frankly, this may be due to continuity errors. Or, perhaps, it's intentional and shows the audience the limitations of the Invisibility Cloak.

An example of why a Disillusionment Charm might be a better choice than an Invisibility Cloak in certain situations comes up in Order of the Phoenix:

‘Come here, boy,’ said Moody gruffly, beckoning Harry towards him with his wand. ‘I need to Disillusion you.’

‘You need to what?’ said Harry nervously.

‘Disillusionment Charm,’ said Moody, raising his wand. ‘Lupin says you’ve got an Invisibility Cloak, but it won’t stay on while we’re flying; this’ll disguise you better. Here you go –’

_{Order of the Phoenix - page 53 - Bloomsbury - chapter three, The Advance Guard}

In Chamber of Secrets when Harry and Ron are hiding under the Invisibility Cloak in Hagrid's hut while Lucius Malfoy and Cornelius Fudge are there, Dumbledore successfully uses the Hominum Reveleo spell to detect Harry and Ron's presence.

‘However,’ said Dumbledore, speaking very slowly and clearly, so that none of them could miss a word, ‘you will find that I will only truly have left this school when none here are loyal to me. You will also find that help will always be given at Hogwarts to those who ask for it.’

For a second, Harry was almost sure Dumbledore’s eyes flickered towards the corner where he and Ron stood hidden.

_{Chamber of Secrets - page 195 - Bloomsbury - chapter fourteen, Cornelius Fudge}

In Deathly Hallows, when Harry et al arrive at Gringott's to break into the Lestranges' vault, Harry seems to have reason to believe Probity-Probes would be able to detect him and Griphook under the Invisibility Cloak, and he stuns the goblin guards before they can use the Probity-Probes:

‘Ah, Probity Probes,’ sighed Travers theatrically, ‘so crude – but effective!’

And he set off up the steps, nodding left and right to the wizards, who raised the golden rods and passed them up and down his body. The Probes, Harry knew, detected spells of concealment and hidden magical objects. Knowing that he had only seconds, Harry pointed Draco’s wand at each of the guards in turn and murmured, ‘Confundo,’ twice. Unnoticed by Travers, who was looking through the bronze doors at the inner hall, each of the guards gave a little start as the spells hit them.

_{Deathly Hallows - page 427 - Bloomsbury - chapter twenty-six, Gringott's}

Invisibility Cloaks are not immune to all forms of magic. In Goblet of Fire, Harry discovers that Mad-Eye Moody's magical eye can see through Invisibility Cloaks.

Moody took a step closer to the foot of the stairs. Harry saw Moody’s magical eye travel over Snape, and then, unmistakeably, onto himself.

Harry’s heart gave a horrible jolt. Moody could see through Invisibility Cloaks ... he alone could see the full strangeness of the scene ... Snape in his nightshirt, Filch clutching the egg, and he, Harry, trapped in the stairs behind them. Moody’s lopsided gash of a mouth opened in surprise. For a few seconds, he and Harry stared straight into each other’s eyes. Then Moody closed his mouth and turned his blue eye upon Snape again.

_{Order of the Phoenix - page 409 - Bloomsbury - chapter twenty-five, The Egg and the Eye}

I think it's interesting the cloak didn't respond to the Death Eaters' Accios in Hogsmeade in Deathly Hallows. Just because Xenophilius Lovegood believed the cloak to be infallible doesn't mean he was right. In fact, canon demonstrates in several places that Harry's cloak is not impervious. Draco Malfoy's Petrifcus Totalus worked on Harry through the Invisibility Cloak because Invisibility Cloaks are not infallible and can be penetrated by some forms of magic.

ETA: 4.2.14 - While researching another question, I found a passage in Deathly Hallows that explains if a person knows where another person who is hiding under an Invisibility Cloak is located, they may successfully cast magic upon the person hiding.

‘I could hardly believe what I was seeing. I asked to borrow [the Invisibility Cloak from James Potter], to examine it. I had long since given up my dream of uniting the Hallows, but I could not resist, could not help taking a closer look ... It was a Cloak the likes of which I had never seen, immensely old, perfect in every respect ... and then your father died, and I had two Hallows at last, all to myself!’

His tone was unbearably bitter.

‘The Cloak wouldn’t have helped them survive, though,’ Harry said quickly. ‘Voldemort knew where my mum and dad were. The Cloak couldn’t have made them curse-proof.’

‘True,’ sighed Dumbledore. ‘True.’

_{Deathly Hallows - page 572-573 - Bloomsbury - chapter thirty-five, King's Cross}

So, I amend my answer to: Draco Malfoy's Petrifcus Totalus worked on Harry through the Invisibility Cloak because Invisibility Cloaks are not infallible and can be penetrated by some forms of magic. Also, if a person hiding under an Invisibility Cloak's location is known, a witch or wizard can curse the person hiding. Draco Malfoy was able to curse Harry with Petrifcus Totalus because he knew exactly where Harry was, even though Harry was wearing his Invisibility Cloak.

Hopefully these two canon-based explanations regarding the Invisibility Cloak -- the reliability of the Invisibility Cloak and the issue of the location of the person wearing the Cloak -- sufficiently answers this question.

Answer 2

Simply said, it's because all the cloak does is provide excellent invisibility. There are many assumptions about it, as a 'Deathly Hallow', but all we really know about it is that it's an unusually potent and durable Invisibility cloak.

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"We are talking about a cloak that really and truly renders the wearer completely invisible, and endures eternally, giving constant and impenetrable concealment, no matter what spells are cast at it."

Harry's cloak does just that, from what we can see.. But that requires you to stay under it, and all it's providing is concealment. No spell cast at the cloak could compromise this (i.e., summoning it (Accio), etc.) but it doesn't prevent someone who knows where he is from casting a spell upon him, as Dumbledore later shows when he paralyzes Harry at a climactic scene. Invisibility doesn't protect you from spells, unless they somehow require the caster to be able to see you directly, and, based on what happens, at least a few don't.

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With thanks to Slytherincess -- here's the supporting quote:

‘I could hardly believe what I was seeing. I asked to borrow [the Invisibility Cloak from James Potter], to examine it. I had long since given up my dream of uniting the Hallows, but I could not resist, could not help taking a closer look ... It was a Cloak the likes of which I had never seen, immensely old, perfect in every respect ... and then your father died, and I had two Hallows at last, all to myself!’

His tone was unbearably bitter.

‘The Cloak wouldn’t have helped them survive, though,’ Harry said quickly. ‘Voldemort knew where my mum and dad were. The Cloak couldn’t have made them curse-proof.’

‘True,’ sighed Dumbledore. ‘True.’

_{Deathly Hallows - page 572-573 - Bloomsbury - chapter thirty-five, King's Cross}

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And Malfoy did know he was there due to Harry's mistakes:

It was fortunate that Goyle and Zabini were snarling at each other, drawing all eyes onto them, for Harry was quite sure his feet and ankles had been revealed as the cloak had flapped around them; indeed, for one horrible moment he thought he saw Malfoy’s eyes follow his trainer as it whipped upward out of sight.

[Emphasis added]

And, if that weren't enough:

Harry was so busy staring at Malfoy, he did not notice Goyle reaching up for his trunk; as he swung it down, it hit Harry hard on the side of the head. He let out an involuntary gasp of pain, and Malfoy looked up at the luggage rack, frowning.

[Emphasis added]

Malfoy didn't cast at the cloak, in an attempt to reveal Harry; he knew where he was and simply cast at him where he knew that he had to be -- no different, really, than casting with his eyes closed.

All that being said, behind the scenes, JKR has contradicted the In-story description of the cloak; she claimed that Dumbledore cast a non-verbal Homenum revelio spell, and that's how he knew Harry was there even under the cloak; that contradicts the 'impenetrable concealment' idea. But that's behind the scenes and never directly stated in the story, so make of it what you will.

Also, as Slytherincess points out, the info we have on it is from an unreliable source; how much of what he says is fact, and how much is legend is open to interpretation. Certainly Harry's cloak seems to last like no other, but beyond that, it's hard to say what is truth and what is legend.

Answer 3

I think you have misunderstood the quote in your question. To say that something "endures eternally" means only to say that it lasts forever. To say that the cloak provides "impenetranable concealment" and that the wearer is "completely invisible" means just that - the person is concealed and invisible. But it does not mean they are impervious to attack. In short, there is nothing whatsoever in that quote to suggest that Harry's cloak should have blocked Malfoy's spell.

In canon, we know of inconsistencies in the cloak's ability to conceal - other answers e.g. that of Slytherincess provide a wealth of information on that topic. But for me the explanation is a simple one: it's an "Invisibility Cloak", not an Invincibility Cloak. Its function is to conceal the person or persons hidden under it, not to protect them from any and all attacks.

Of course, that leaves the issue of Accio not working on the cloak, which I believe is the real inconsistency here. I cannot explain that and will happily defer to others, if they have a better researched answer. Pure speculation: perhaps, as the cloak is part of Death's cloak, that is what makes it resistant to the Accio charm. We might further speculate that Death's cloak has no powers of protection against spells used against Death, as he has no reason to need such protections. Or alternatively, perhaps it's just not possible to magically summon the clothes off of somebody's back (just imagine the chaos that might cause!). But I best leave it at that lest somebody thinks this answer is too speculative.

Answer 4

Given that it was a curse focused on Harry himself, rather than the Cloak, it makes perfect sense that it would work - the cloak is immune to curses, but the wearer is not protected by them just from wearing the cloak.

Answer 5

From the Harry Potter Wiki article, Cloak of Invisibility:

Although powerful, the Cloak of Invisibility is not infallible. While the Cloak itself resists spell damage, it does not shield the wearer from spells used against them personally. For example, Harry was immobilized while under the Cloak twice during the 1996–1997 school year. In addition, it will not hide the wearer from detection that is not based on optical sight, such as Alastor Moody's magical eye, magical creatures such as Dementors, spells such as the Human-presence-revealing spell, the Marauder's Map, or (arguably) certain Dark Detectors (e.g. Sneakoscopes would presumably still detect an untrustworthy action performed under the Cloak, and it's possible - but uncertain - that the Cloak would be detected by Probity Probes).

Answer 6

Harry's cloak is described as being particularly durable and permanently invisible, but there is not a mention of it being able to deflect spells that are cast at the wearer of the cloak. If a spell were cast at the cloak commanding it to reveal itself, it would deflect the spell, but a curse directed at the person underneath it is not going to be held back.