Muggles' Guide to Harry Potter/Major Events/Severus' Death

Overview
In the belief that the Elder Wand will grant its allegiance only to one who has slain its previous owner, Lord Voldemort has his pet snake, Nagini, kill Severus Snape.

Event Details
Through the confusion of the Battle of Hogwarts, Hermione notices that there does not seem to be any sign of Voldemort. She asks Harry to try and look into his mind, to see where he is. Harry looks into Voldemort's mind, and sees Voldemort ordering a bedraggled-looking Lucius Malfoy to fetch Snape to him. Returning to himself, Harry tells Hermione and Ron that Voldemort is in the Shrieking Shack.

Making their way through the tunnel to the Shrieking Shack, the Trio find their way into the Shack blocked by boxes. Hidden by these boxes, they listen (and Harry watches) as Snape reports to Voldemort. Snape seems to be asking permission to enter Hogwarts and fetch Harry out for Voldemort. Voldemort, however, has something else on his mind and summarily dismisses Snape's request. He says that the Elder Wand that he has retrieved from Dumbledore's tomb is a fine wand, but is nothing special. He says that he believes that the wand is not performing to its best ability because it has not yet shifted its allegiance to him. And why not? Because Snape killed Dumbledore, and so the wand currently owes its allegiance to Snape. The wand will not perform its best for Voldemort until Snape is dead. So saying, Voldemort waves his pet snake, Nagini, in her nest of protective spells, into Snape. Nagini immediately bites Snape, who falls. Voldemort and Nagini leave the room; Harry pushes the boxes aside and kneels over the fallen Snape. Seeing Harry, Snape forces a large quantity of memories out of his head, and Harry collects them in a crystal flask that Hermione provides. Then, asking Harry to look into his eyes, Snape dies.

Notable Consequences
The memories that Snape has provided to Harry will prove, once and for all, where his loyalties have lain for the entire series. The viewing of these memories explains much of why Snape has acted the way he has throughout the series, and will affirm Dumbledore's trust of Snape.

The memories Harry has received will also give Harry the necessary information he needs to finally defeat Voldemort.

The death of Snape leaves Voldemort confident in having finally gained the full powers of the Elder Wand. This faith may be misplaced.

Analysis
As we will find out, there is really a large amount of information that Snape feels the need to pass to Harry. There is no way that Snape could have told it all to Harry in the midst of the battle, and in fact there is little way that Harry would have been prepared to believe anything that Snape, a Death Eater deep within the councils of Voldemort, could have told him. Yet, despite the battle proceeding apace, Harry must get this information. Snape's death, and the immediate crushing urgency of getting the message to Harry, is likely the only way that Snape could have gotten these memories to Harry in the available time, and likely the only way that Harry could have accepted them.

Greater Picture
The key piece of information that Harry receives from Snape is that a fragment of Voldemort's soul is lodged within Harry, and that the only way to dislodge it, and thus prevent Voldemort from returning again, is to have Voldemort kill Harry. Snape has been charged with passing this message on by Dumbledore, once Voldemort stops sending Nagini out to run his errands, instead keeping her close and magically protected. This actually is one link in the chain which almost fails. While Dumbledore does generally plan for the occasional failure, he had somehow assumed that once Voldemort had started protecting Nagini, Snape would still have the necessary freedom of motion to be able to pass the message on to Harry. Dumbledore had clearly not been aware either that Voldemort would so lightly kill his main lieutenant, or that the animosity between Snape and Harry would be increased by Dumbledore's death to the point that Harry would actually have killed Snape given the chance. If Harry had not been present at Snape's death, or if he had not been restrained from killing Snape by the presence of Voldemort and Nagini, the message would never have been passed, and the one remaining soul shard would have remained, anchoring Voldemort to the earth and to Harry.

Several additional pieces of Snape's memory come along with that one fact, however. Snape evidently feels the need to explain himself, and his actions. We learn that Snape had acted out of unrequited love for Harry's mother, Lily Evans. It is likely that it was necessary for Snape to include that background; it is uncertain whether Harry would have believed him, even given the memories, if he had not had that information about why Snape had acted as he did. Without that information, the ties holding Snape to the Order of the Phoenix seem far too tenuous to make us believe in them, and we would continue to believe, as Harry has, that Snape's first loyalty is to Voldemort. Given that belief, anything Snape could say would be seen as serving the interests of Voldemort, rather than of Harry. Harry, feeling that Snape had duped poor, trusting Dumbledore as he had everyone else, would equally distrust anything Snape told Dumbledore, making the memories of Snape and Dumbledore's discussions also entirely suspect.

Harry, having seen these memories, recognizes that Snape was a strong wizard, true to his given word no matter how distasteful the duties he was assigned, and was acting throughout in Harry's best interests, at Dumbledore's request. As we will find out in the epilogue, Harry eventually names one of his children after both Snape and Dumbledore.