Lord Voldemort callously fed Muggle Studies teacher Charity Burbage to Nagini after performing the Killing Curse. Sometimes Voldemort simply let Nagini do the dirty deed herself.
Charity Burbage floats helplessly above a dinner table, as if paralysed. She begs Snape to help her. Voldemort point his wand at her, and a green light erupts out of its end. The light hits Charity, and she falls down on to the table dead, her eyes open and her face splattered with droplets of blood.
During this time, Voldemort killed a witch called Bertha Jorkins, and J. K. Rowling confirmed it was through her murder that he turned Nagini into a Horcrux. But Nagini was reintroduced in Fantastic Beasts: The Crimes of Grindelwald, which complicated the previous assumption that he'd met her in Albania.
The more reliable yet gruesome explanation is that Voldemort killed Bathilda, reanimated her corpse through magic and then hid the snake inside.
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.
Voldemort had a special relationship with Nagini, as she was his pet and one of his Horcruxes. According to Dumbledore, Voldemort had strong feelings for Nagini that he had not for anyone else; she was the one living thing that he had ever cared about.
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.
Behind the scenes. 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.
Bagshot is best known for writing Harry's History of Magic textbook. In the weeks after Dumbledore's death, Rita Skeeter preyed on Bagshot's old age and failing mind to conduct invasive interviews on the Dumbledore family.
Despite persistent questioning, Bathilda did not say anything to Harry or Hermione, instead beckoning for Harry to follow her upstairs.
Unless one or the other has a significantly smaller role in the films than we are led to believe, Dumbledore and Nagini will get to know each other. From the very little we see of Nagini, it looks like she's at least potentially on the same side as Dumbledore.
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'.
At the end of the last film, Grindelwald told Credence he was really Aurelius Dumbledore – the previously unheard of sibling of Albus. However, that wasn't entirely true. While Credence is a Dumbledore, he isn't the brother of Albus, Aberforth and Ariana. In fact, he's Aberforth's secret son!
Bathilda is a very old witch and the former neighbor of the Dumbledore family in Godric's Hollow. As such, she knows quite a bit about the family's past, including the darker and more tragic parts. As the great aunt of Gellert Grindelwald, it was actually Bathilda who introduced Dumbledore to the future Dark wizard.
Myrtle Warren was once a Hogwarts student, but after her untimely death, she stayed back as a spirit to eternally haunt the second-floor girls' bathroom. Myrtle had a hard time at Hogwarts, and was frequently bullied. Prone to wailing morosely, the ghost became known informally as Moaning Myrtle.
Isaacs brings up Lucius' disheveled appearance in Deathly Hallows, raising the possibility that the Malfoy patriarch had begun drinking too much. The way Isaacs saw it, Lucius was in a no-win situation. Given everything he'd done, the man no longer had a place on either side of the war.
Moreover all she could hear would be hissing from the other room which can easily be disregarded. That is why Bathilda didn't speak in the same room as Hermione otherwise she would have made the connection that the hissing sound is actually coming from Bathilda herself.
Bathilda Bagshot was very old around the time Rita Skeeter came to interview her. After Rita left, Bathilda died a few days later. Lord Voldemort used Dark Magic to reanimate Bathilda Bagshot's corpse and then made Nagini enter her corpse, thereby giving her control of the movements of the corpse.
Bathilda Bagshot has actually been dead for weeks, which explains the flies and blood handprints Hermione finds. Her body has been inhabited by Nagini, Voldemort's snake put there to trap Harry because Voldemort suspected, just as Hermione said, that Harry would return to the town where he was born.
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.
Her corpse was then animated by Lord Voldemort to contain his pet snake Nagini. This was intended to be a trap for Harry Potter. Bathilda was also the great-aunt of Gellert Grindelwald, the infamous Dark wizard who was defeated by Albus Dumbledore.
He was afraid that the Elder Wand, recognizing his true owner, wouldn't work as intended, or worse, backfire on him. Giving Nagini the order to kill, indirectly would have led him to win the Wand's allegiance as per him, without any side-effects.
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.
So it's possible that Nagini met Tom Riddle in his early years of rising to power but by the time she found him in Albania she had been cursed to become a snake entirely, and losing the ability to turn back into a human.
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.