A/N: Any animals mentioned are strictly based on the information given about them in the main 7 books and the "Fantastic Beasts & Where to Find Them" book, not from the Fantastic Beasts movies (because I haven't seen them).
"So what exactly is the use of a Bumblethorn, Luna?" Harry asked casually at supper one night. They were sitting at the Gryffindor table in the Great Hall, enjoying a delicious chicken pot pie made by Dobby, Kreacher, and the rest of the Hogwarts house elves.
It was a few weeks after he and Hermione had helped Luna find her Bumblethorn necklace in the Forbidden Forest, and whenever she had sat down at the table a few minutes earlier, he'd noticed she was wearing it again. Despite being a Ravenclaw, Luna had started sitting at the Gryffindor table with Harry and Hermione most of the time, since they were nicer to her than most of the other students in the school were, and they made sure no one at the Gryffindor table was mean to her when she sat with them.
Now Harry wasn't actually particularly interested in what a Bumblethorn was for, but Ron had been going on and on about the Chudley Cannons' recent upset victory over the league-leading and three-time defending champions, Puddlemere United. And as much as Harry liked quidditch, if he had to listen to Ron's story for the fifth time that day, and the twentieth time since the Cannons had won, he was going to explode. Or make Ron explode; he was quite sure Hermione could tell him what the necessary spell was (and based on the look on her face as Ron launched into the story for the eighth time that day, would be more than happy to do so). But getting Luna to talk about her necklace seemed a lot less likely to result in a massive loss of House Points than blowing up Ron would (and Snape had been on the prowl over the past couple days for any Gryffindors with even the smallest toe over his made-up line) — not that House Points earned and lost during the year actually mattered a lick when Dumbledore gave out the House Cup at the end of the year.
"Oh, this?" replied Luna, lifting up the rotten, moldy, tomato-looking thing that was hanging on an intricate silver chain around her neck.
Harry and Hermione settled back to enjoy the show.
As Luna began telling Harry all about her Bumblethorn necklace, Ron started talking louder so that no one would miss any of the highly important details of his super-exciting and nerve-wracking Chudley Cannons story. Luna, on the other hand, since she was just telling Harry what a Bumblethorn was, kept her normal, quiet, dreamy pitch that she always talked in; and yet somehow, every person within ten seats of Luna suddenly realized she was telling a story that didn't have to do with quidditch — and specifically the Chudley Cannons — and instantly focused all their attention on her. After all, any far-fetched story of Luna's had to be better than hearing for the tenth time that day how the Chudley Cannons had beaten Puddlemere United.
As usual when Luna was talking about something only she and her father believed in, Harry only half payed attention to what she was actually saying. But what he did get from Luna's tale was that a.) Bumblethorns are native to somewhere not around there, b.) they are extremely rare (wow, what a surprise), and c.) they are supposedly really good at repelling occamy.
Now what risk Luna had of encountering an occamy in Scotland in order to need to wear a Bumblethorn, Harry wasn't exactly sure, since occamy only live in the Far East, but whatever made Luna happy.
That weekend, Harry and Hermione were hanging out together on the far side of the lake, away from everyone else where they couldn't be bothered. It was likely to be one of the last nice days of fall before it turned cold, so they were making the most of it. They had been there most of the morning when Luna came aimlessly wandering up, absentmindedly twirling her wand in her fingers.
"Hi guys," she said when she saw them.
"Hi, Luna," replied Harry and Hermione together.
"I was about to go for a walk in the northern woods past the school grounds. Want to come along?" asked Luna, sticking her wand behind her ear for safekeeping.
Harry and Hermione looked at each other, and shrugged.
"Sure, why not," said Harry, looking back up at Luna.
An hour later, they'd made their way past the boundary of the school, and had been hiking through the woods on the north side for a good thirty minutes. The woods were fairly open and easy to walk through, unlike the Forbidden Forest inside Hogwarts.
They had just crossed over a small stream, when suddenly in front of them appeared what looked to be a ten foot long serpent, great, shining, and as green as poison; except it was hovering four feet off the ground, slowly flapping large, luscious, magenta-colored wings, and had a dark purple plume coming off the back of its head. It also had two spindly, bird-like legs tucked up under the middle of its body, but none of them were looking there to notice.
Harry and Hermione instantly pulled out their wands and leveled them at the creature. Luna removed her wand from behind her ear, and held it loosely by her side. The serpent bared its fangs at them, giving them a good view of its long, sharp, poisonous fangs that reminded Harry a little too much of a basilisk's fangs, though substantially smaller.
As they stood in a stand-off, wizards with their wands held ready, and flying serpent with its fangs bared, Hermione quickly stole a glance around to get a better lay of their predicament; a gleam of silver caught her eye, coming from a large pile of sticks that looked very nearly like a large nest.
"Um, Luna?" Hermione began hesitantly, "That wouldn't happen to be an occamy, would it?", nodding towards the creature.
"Looks kind of like one," replied Luna contemplatively. "But it also could be a flubberhorn. They look very similar. Flubberhorn's aren't at all dangerous, though. They're quite nice really, and —"
"And you wouldn't happen to be wearing your Bumblethorn necklace that can repel occamy, would you?" interrupted Hermione in a slightly higher-pitched voice as the winged serpent slowly fluttered nearer to them, fangs still bared, tongue flickering in and out threateningly.
It wasn't that she actually believed a Bumblethorn (or whatever it really was) could scare away an occamy, but at the moment she was willing to give anything a shot, since their only alternative was to attempt to fight it, and even with all three of their skills combined, she wasn't sure that was a fight they could win.
"Oh, yes, of course," said Luna, tucking her wand back behind her ear, and leisurely pulling the Bumblethorn out from under her outer cloak.
Pulling the silver chain from around her neck, she held it up as high as she could in front of her, and casually began walking towards the occamy. Harry and Hermione held their wands tight, ready to send curses towards the beast if it attacked her. But its attention seemed to be focused entirely on the large, red, moldy fruit. When she got about ten feet away from the creature, Luna began swinging the Bumblethorn gently, and singing softly in a language neither Harry nor Hermione could understand; if it was in fact actually a language — Harry thought it sounded more like humming, if humming had words.
After a few seconds, the occamy began slowly fluttering slightly backwards, before suddenly spinning around in the air and shooting straight up and away from them, at quite a surprising pace for a serpent with wings.
They watched it fly away over the trees for a several seconds to make sure it was really leaving, before Harry and Hermione simultaneously released the breaths they'd been holding, and Hermione rushed over to Luna and flung her arms around her in a giant hug.
As they walked back towards the castle grounds, Harry leaned over and whispered to Hermione, "Well, I'll never doubt one of Luna's crazy theories again. Maybe she's even right about all those fantastic beasts she goes on about that none of us believed existed. Nargles included."
A/N: If you liked this, and want to read something similar, check out "Late One Night," which would be a prequel if read in this order. Or if this story helped you procrastinate doing whatever you're actually supposed to be doing right now, and you'd like to further procrastinate, then go read that one.