Nagini's lifespan was extended by being a horcrux. Nagini's lifespan was extended by other magic. Nagini spent some time in suspended animation and did not age. (perhaps while Voldemort was “dead”)
It's later revealed that Nagini was never an ordinary magical snake from start, as she was once in fact, a human (possibly a Witch) who became a snake as she is now as result of a blood curse and trapped in that form for the rest of her life.
Lord Voldemort and Nagini had a special relationship
As a Parselmouth, (i.e. able to talk to snakes) Voldemort could communicate with her, and the pair often sent each other messages, even suggesting a telepathic connection at times.
Rowling previously revealed that Nagini is a Maledictus, which means she carries a blood curse that will doom her to transform permanently into a beast.
Fact: Nagini Was Around 100 Years Old When She Died
This would put her age anywhere from mid 90s or early 100s when she was finally killed. While not unheard of for magical individuals to have long lifespans, it's still remarkable to think of her living that long in snake form.
Nagini is loyal to Voldemort because he can speak with snakes. As a Maledictus, there probably isn't much time after the events in The Crimes of Grindelwald before Nagini falls to her blood curse, becoming a snake forever.
By 1994, Nagini was seemingly trapped in snake form and belonged to Lord Voldemort, with whom she had a special bond largely due to becoming a Horcrux after her master had killed Bertha Jorkins in 1994.
Harry can no longer speak it
Harry being an accidental Horcrux meant he was bound to Voldemort in so many ways, just like Voldemort was bound to serpents. Not only could Harry speak the language of the snake, but could see through the eyes of Nagini, another of Voldemort's Horcruxes, as it turned out.
Dumbledore does not use any language to make one think that Nagini is anything more than a snake. But this could be despite his knowledge of Nagini's past because he has to factor his grand plans into everything he tells (or doesn't tell) Harry.
When Harry and Hermione are on the first floor of Bathilda's house, Nagini (inside the corpse of Bathilda) tells Harry to "Come!" from the next room in Parseltongue. In reaction, Hermione jumps and clutches Harry's arm, and the two of them obey the command.
She was dieting and didn't want greasy food.
It wasn't just inanimate objects that could become Horcruxes. Lord Voldemort's beloved snake companion, Nagini, was also transformed into one, and Dumbledore seemed to know it, ominously predicting that a day would come where Voldemort would 'fear for his snake'.
Deathly HallowsEdit
Nagini, Voldemort's snake, then eats Professor Burbage's dead body. A story about her "resignation" from Hogwarts appears in the Prophet, but members of the Order of the Phoenix discount it, as they are unable to locate her anywhere after that.
Albus confirms to Creedence early on in the film that he is in fact a Dumbledore, quashing any rumor that Grindelwald had lied to the young boy in order to sway him to his movement. It is explained that Credence is the illegitimate son of Albus's younger brother, Aberforth (Richard Coyle).
Nagini, it turns out, was actually a Maledictus—a witch with a blood curse that turns her permanently into a beast (in her case, a giant snake). In the film, the witch is played by Claudia Kim.
Though it may later be revealed that the Dark Lord did indeed know that Nagini was a Maledictus, there's currently no indication that he (or anyone else) ever thought that she was anything other than a snake who was made into one of the Dark Lord's Horcruxes.
Because Nagini also happens to be the name of another iconic “Harry Potter” character — Lord Voldemort's magical, extremely murderous pet snake. Well, just in case there was any doubt, “Harry Potter” creator JK Rowling confirmed the two characters are one and the same.
In the movies, Nagini was the one who killed Snape in the boathouse. The Maledictus meets her end when Neville Longbottom finds Gryffindor's sword and, in an attempt to destroy the final Horcrux, cuts off her head.
There was a rumour that Nagini was the snake Harry released from the zoo in Harry Potter and the Philosopher's Stone. This was proven false, as Nagini is some type of viper while the snake in the zoo was a boa constrictor. Furthermore, the snake was given a male voice in the film, while Nagini is female.
But JK Rowling tweeted that Nagini is based on "the Naga", which are "snake-like mythical creatures of Indonesian mythology." She added: "They are sometimes depicted as winged, sometimes as half-human, half-snake. Indonesia comprises a few hundred ethnic groups, including Javanese, Chinese and Betawi."
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. If Quirrell had killed Harry right away, he would have lost the chance to get the stone.
Avada kadavra spell can be blocked by objects like statues, etc. (OoP). Now, Voldemort had already split his soul into different parts i.e. horcrux. So basically he had become immortal and therefore using the spell would not harm him.
Nagini appears as a human character in the movie "Fantastic Beasts: The Crimes of Grindlewald", where it is revealed that she had a blood curse that would eventually turn her permanently into a snake. I don't think her becoming Lord Voldemort's "pet" was by her choice. Thank you so much!
Nagini is the last Horcrux that Voldemort created and the last one to be destroyed. During the final battle of Hogwarts, Neville pulls the sword of Godric Gryffindor from the Sorting Hat and beheads Nagini, destroying the last Horcrux.
Norris being a Maledictus is her relationship with Hogwarts staff member and caretaker Argus Filch. The two are introduced together in both the Harry Potter movies and books. The pair take a divide and conquer method when it comes to tracking down any rule-breaking students.