Can legilimency be felt?

Question

In Harry Potter and the Order of the Phoenix, when Snape is teaching Occlumency to Harry, not only can Harry feel the attacks, but he could be said to be getting tired of it.

“I am about to attempt to break into your mind,” said Snape softly. “We are going to see how well you resist. I have been told that you have already shown aptitude at resisting the Imperius Curse. . . . You will find that similar powers are needed for this. . . . Brace yourself, now. . . . Legilimens!” Snape had struck before Harry was ready, before Harry had even begun to summon any force of resistance: the office swam in front of his eyes and vanished, image after image was racing through his mind like a flickering film so vivid it blinded him to his surroundings . . He was five, watching Dudley riding a new red bicycle, and his heart was bursting with jealousy. . . . He was nine, and Ripper the bulldog was chasing him up a tree and the Dursleys were laughing below on the lawn. . . . He was sitting under the Sorting Hat, and it was telling him he would do well in Slytherin. . . . Hermione was lying in the hospital wing, her face covered with thick black hair. . . . A hundred dementors were closing in on him beside the dark lake. . . . Cho Chang was drawing nearer to him under the mistletoe . . . No, said a voice in Harry’s head, as the memory of Cho drew nearer, you’re not watching that, you’re not watching it, it’s private — He felt a sharp pain in his knee. Snape’s office had come back into view and he realized that he had fallen to the floor; one of his knees had collided painfully with the leg of Snape’s desk.

"Hermione told me to come and check on you," said Ron in a low voice, helping Harry to his feet. "She says your defenses will be low at the moment, after Snape's been fiddling around with your mind... Still, I suppose it'll help in the long run, won't it?"

^{Harry Potter and the Order of the Phoenix}

Harry, seems to lose view of his surroundings

"Snape’s office had come back into view"

and be unaware of what is going on around him. That could be due to the fact that he is trying to resist, though, he wasn't really ready. He finds himself with one knee bent, implying that he was not even in full control of his body.

On the other hand, it seems that when Lord Voldemort is using Legilimency, it usually not felt. None of the characters it is used on screams, shouts, lose control over their body, look suffering or tiered, lose awareness, or even hinted to be aware of what happened.

"Now...why don't you give me that Stone in your pocket?"

"He lies...He lies..."

^{Harry Potter and the Philosopher's Stone}

Wormtail:"But you seem so much stronger, My Lord —"

Voldemort:"Liar"

Wormtail:"I — I thought she might be useful, My Lord —"

Voldemort:"Liar"

"You have no wife", said the cold voice, very quietly. "Nobody knows you are here. You told nobody that you were coming. Do not lie to Lord Voldemort, muggle, for he knows... he always knows..."

“Do not lie to me!” hissed the second voice. “I can always tell, Wormtail!”

^{Harry Potter and the Goblet of Fire}

"So, you smashed my prophecy?" said Voldemort softly, starting at Harry with those pitiless red eyes. "No, Bella, he is not lying... I see the truth looking at me from within his worthless mind... months of preparation, months of effort... and my Death Eaters have let Harry Potter thwart me again..."

"Do not lie to Lord Voldemort, Gregorovitch. He knows... he always knows."

^{Harry Potter and the Order of the Phoenix}

So, can it be felt? Maybe Lord Voldemort is so much better than Snape that he can do it without it being felt while Snape can't? Maybe they are not doing exactly the same thing?

Answer 1

Let's start with the definition of Legilimency. It is presented by Snape during his first private lesson with Harry:

“It is the ability to extract feelings and memories from another person’s mind —”

“Only Muggles talk of ‘mind reading.’ The mind is not a book, to be opened at will and examined at leisure. Thoughts are not etched on the inside of skulls, to be perused by any invader. The mind is a complex and many-layered thing, Potter... or at least, most minds are...” He smirked. “It is true, however, that those who have mastered Legilimency are able, under certain conditions, to delve into the minds of their victims and to interpret their findings correctly. The Dark Lord, for instance, almost always knows when somebody is lying to him. Only those skilled at Occlumency are able to shut down those feelings and memories that contradict the lie, and so utter falsehoods in his presence without detection.”

It seems that to perform Legilimency is not simply to cast a spell. It is a complex process and as such can be performed thoroughly or superficially.

Author of the question gave good quotes of Voldemort detecting lies. Let me give one another:

“Saturday... at nightfall,” repeated Voldemort. His red eyes fastened upon Snape’s black ones with such intensity that some of the watchers looked away, apparently fearful that they themselves would be scorched by the ferocity of the gaze. Snape, however, looked calmly back into Voldemort’s face and, after a moment or two, Voldemort’s lipless mouth curved into something like a smile.

Everybody in the room was aware of intense gaze of Voldemort, including Snape - the Master of Occlumency.

There is also another quote from Half Blood Prince:

(...) don’t look at me like that! I know what you’re doing, I’m not stupid, but it won’t work — I can stop you!” There was a pause and then Snape said quietly, “Ah... Aunt Bellatrix has been teaching you Occlumency, I see.

Draco Malfoy was able to realize that Snape was performing some kind of Legilimency on him.

Let me risk one another quote:

Dumbledore was giving Harry a searching look. His twinkling light-blue gaze made Harry feel as though he were being X-rayed. “Innocent until proven guilty, Severus,” he said firmly.

I believe Dumbledore uses the same technique occasionally on Harry. It happens several times throughout the books and Harry always describe the feeling like him being X-rayed.

On the other hand Harry lost control over himself every time Snape tried to read his memories. There are also examples of people loosing their mind (or life) after their memories had been forcibly extracted (Bertha Jorkins).

My conclusion is that if a Wizard performs shallow Legilimency (like only searching for the symptoms of lie) it is not much different from just an intense gaze. But the deeper the Legilimency (like reading memories) the deeper it is felt by its subject.