Even by Voldemort's logic, Snape wasn't the rightful owner of the Elder Wand. Voldemort thought that the wand passed based on needing to kill the person who previously owned the wand. He therefore kills Snape, since Snape killed Dumbledore.
We know the Elder Wand allied with Draco Malfoy, who disarmed rather than killed Albus Dumbledore. It later switched its loyalty to Harry Potter during his escape from Malfoy Manor.
Why didn't Dumbledore tell Snape about the Elder Wand so Snape could break it before Voldemort found it? The answer is simple: It was far too risky for Severus Snape to be aware of both the Hallows and the Horcruxes.
Probably, Snape knew ownership of the elder wand had passed to Draco because he disarmed Dumbledore the night he was killed. The books never indicated Snape was aware the ownership had passed to Harry.
Snape was never the Elder Wand's Master, so Voldemort killing Snape was pointless. Ownership of the wand then passed from Draco to Harry Potter, when Harry physically overpowered Draco and stole his wand from him, simultaneously claiming ownership of both Draco's own wand and the Elder Wand.
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised.
In order to conjure the avada kedavra curse, you have to want to kill your victim. We all know that Voldemort could easily kill a child without an ounce of remorse... but not Snape. Snape didn't want to kill Dumbledore, and this was why the spell was blue instead of the usual green.
So, Voldemort had to kill Snape for the wand's allegiance to switch. Voldemort knew he couldn't cast Avada Kedavra with the Elder Wand to kill its master, so he ordered Nagini to be the one who killed Snape. In reality, the Elder Wand belonged to Draco, as he was the one to disarm Dumbledore in the Astronomy Tower.
Defeating The Dark Lord with his signature spell
Disarming is about defence, not murder. Voldemort was a killer, Harry was not. It was an important distinction for Harry, who had learned so much about Voldemort and seen first-hand the ways in which they were similar.
He was on the point of collapse when it happened,” Rowling said. “Dumbledore didn't want to lose his wand at that point and Draco disarmed him. So that meant that the wand gave Draco its allegiance, even though Draco never knew it, even though Draco never touched it.
Similarly to Harry, Snape's patronus represents a person. In the memories he gives Harry before his death, Snape shows Dumbledore his patronus, using the form to prove his love of Lily Potter, Harry's mother.
This nuance was lost on Lord Voldemort, who wrongly assumed Severus Snape held the Elder Wand because he was Dumbledore's killer, when in reality Draco had disarmed Dumbledore before Snape arrived on the scene, making Malfoy the wand's true new owner.
Now, as firmly established, Snape was not the greatest fan of Harry, but that didn't mean that he ever stopped loving Lily. Dumbledore was surprised that Snape seemed to care for the boy. With a swish of his wand, Snape conjured up a Patronus – Lily's Patronus, a doe. 'Always,' he said.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
The answer is simple: It was far too risky for Severus Snape to be aware of both the Hallows and the Horcruxes. You have to remember that Severus has his poker face turned on to expert level when he is employing Occlumency in the face of Voldemort, the greatest Legilimens.
8 Hermione Granger: Alohomora
If there is a spell to encapsulate the asset Hermione is to everyone's favorite magical trio, it has to be Alohomora. Alohomora is, fittingly, the spell that is used to unlock locks.
The Killing Curse is a spell that causes instantaneous death and is one of the three Unforgivable Curses. Its incantation is Avada Kedavra. The only known counter-spell is sacrificial protection, which uses the magic of love.
Why doesn t Harry use Avada Kedavra on Bellatrix? Harry didn't use that spell because he cannot bring himself to kill anyone. He is not a killer.
Because Minerva was his friend and they were fighting on the same side (even though she didn't know). So, even when Minerva was duelling to kill, he wasn't, and if he had kept on fighting he might have been forced to hurt her. He deflected every attack quite easily, even when Flitwick joined the fight.
It's a word that gained so much more clarity and tragedy after Harry Potter and the Deathly Hallows revealed that the nefarious Professor Severus Snape was actually serving a nobler cause: protecting Harry from Voldemort out of love for Snape's childhood friend Lily Evans.
Another possibility is that Snape is aware of the origin of the hex Harry cast upon Draco. Snape's immediate demand to see Harry's Potions book suggests strongly that Snape knows where the Sectumsempra spell originated, and also perhaps that he is its original author.