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.
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.
Voldemort has no wish to know anything about anyone outside of himself. It simply wasn't important to him as it didn't give him any power or knowledge. However, it may have helped him use her as a Horcrux possibly because Nagini being formerly human may have helped her be strong enough to become a Horcrux.
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.
Nagini (d. 2 May 1998) was a Maledictus cursed to transform into a snake. Originating possibly in Indonesia, by 1927 she was a performer at the Circus Arcanus where she met Credence Barebone and had a romantic relationship with him.
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.
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.
Nagini seemed integral to Lord Voldemort's survival before he could be restored to his body, and we learnt, quite grotesquely, that Voldemort even tasked Wormtail to 'milk' Nagini so he could live off her venom to keep his strength up.
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.
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.
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'.
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. Burbage is later replaced as Muggle Studies teacher by Alecto Carrow.
After Voldemort was gone, Nagini decided to follow her dreams. She went to Brazil to join other snakes in the Amazon rain forest. While there, her adventures with Voldemort inspired her to write a song in Parseltongue called "I Thought You Were Pretty Cool But Then You Couldn't Even Defeat a Baby.
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.
Nonetheless, despite her initially benevolent nature, Nagini's blood curse eventually turned her into a snake permanently. Though it is unknown if she became evil as a result of that, or was turned evil as a result of Voldemort turning her into a Horcrux. As a snake, Nagini was completely loyal to Lord Voldemort.
But now we know Nagini was no simple supervillainous pet, but a human woman cursed with the “Maledictus” blood curse, which, according to Rowling, is a female-only inherited condition which grants the affected individual the ability to transform into an animal at will, until one day, the transformation becomes ...
no! they were all busy killing the enemy's troops and so was Nagini. it takes a long time for a snake to digest the food it has swallowed.
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.
7 horcruxes were diary, ring, locket, cup, tiara, Nagini and Harry. They were destroyed by Harry, Dumbledore, Ron, Hermione, Crabbe, Neville and Voldemort respectively. Amongst them, only Neville and Crabbe didn't know what Horcrux actually were.
Why did Voldemort have Nagini kill Snape instead of doing it himself? Because he thought he couldn't do it himself. Voldemort was holding the Elder Wand, but thought that its true allegiance laid with Snape, as he was the one who had killed Dumbledore, its previous owner.
Therefore, when Voldemort used the killing curse against Harry in Deathly Hallows - Part 1, he was actually killing part of his own soul, and Harry was able to survive. And after Neville killed Nagini, all Horcruxes were destroyed.
He was given a Blood-Replenishing Potion, as he continued to bleed profusely any time his bandages were removed, suggesting that Nagini's venom somehow prevented or delayed blood clotting.
Funnily enough, the most famous Lestrange is one only by marriage, and despite really adorable Instagram photos that make us wish it so, there is no blood relation between Leta and Bellatrix whatsoever. At most, Leta and Rodolphus Lestrange (Bellatrix's husband) are very distant cousins.
Nagini's Future After The Fantastic Beasts Movies
From that point on, she goes to the forests of Albania, presumably to live out the rest of her life as a gargantuan creature, perpetually bound in her scaly form.
“Yes, it's rather funny, really, that next to no-one realised the snake that Harry set free in Philosopher's Stone turned out to be Voldemort's final Horcrux, Nagini.” — J.K. Rowling. However, both the zoo snake and Nagini were played by pythons in the movies.