Kaylie and the Boggart
Consider the boggart.
A boggart is a creature whose only point to existing is to scare people. It does not breed; boggarts are immortal, and all the boggarts there are, are all the boggarts there is. It does not eat; no boggart has ever been seen at an all-night fish shop. It is not social; you'll never find four boggarts playing bridge. It is not intelligent; no boggart ever developed a Boggart's Theory of Anything, or won a school science fair.
Boggarts are simply shape-shifting creatures who try their best to bring unreasoning terror to any human they come into contact with. After their victim has run away, they simply return to some sheltered dark place and wait for the next one to come along.
They're rather like the tax man.
And the thing about boggarts is, they've been around humanity so long, even Muggles have learned how to deal with them.
Consider the little girl.
Not little girls in general, but this little girl in particular. Her name is Kaylie. She's seven years old according to the calendar, and about 45 in cynicism. She's an only child, and anyone who's met her knows why; one Kaylie is more than enough for anyone.
Kaylie is an extraordinary child, because people have actually taken the time to teach her to think. Most people don't bother; it's too much trouble generally, especially when there are some really good stubborn opinions and unconscious prejudices to do the job for you. But Kaylie's parents had managed to pass on a gift for critical thought, and in spite of the best efforts of Education, had managed to keep it.
Consider reassembling.
The boggart began pulling itself back together as the twilight deepened into dark. It had spent most of the day discorporate, having been banished from a rather small wardrobe earlier in the day. The wizard who'd done it had been almost contemptuous in the way he shouted "Ridikkulous" and then laughed. The boggart was still offended by it, as much as a boggart can feel offended.
When it had finally pulled all its various bits back together, the boggart went off to find a new home. This was a small town, and it had already been banished several times; boggarts cannot return to a household where they've been banished. It soared through the night, resembling a rather dirty fog, looking at various houses and trying to decide whether they were worth investigating.
It finally found one near the edge of town, an old rambling house more than a century old. The boggart slid down one of the five chimneys, coming out in a large dining room which was empty. It quickly found its way to the cellars, and started to look around.
There were many delightful places for it to take up residence. There was a rather large cupboard next to a washtub that offered plenty of room and contained a number of spider webs. There was also an old oak wardrobe in a small servant's bedroom; a bit small, but comfortable nonetheless. A workroom offered a large number of cabinets, but as they all seemed to be full of tools, supplies of nails and screws, and other maintenance and construction items, the boggart dismissed them from consideration.
Upstairs was also good. There was a nice roll-top writing desk in the sitting room, as well as another of oak wardrobe containing coats and other outdoor gear. Cabinets in the kitchen were too full of dishes or food, and were ignored, although a nice size pantry offered temptation. But what finally attracted the boggart was an upstairs bedroom, with a very large bed that sat high off the floor on a tall brass bed frame.
The boggart floated around underneath the bed for a while, examining it from all angles, and finally decided that this was where it would stay. The comforter hung almost all the way to the floor, making it nice and dark even if the lights were on.
Consider contact.
Kaylie and her mother walked up the stairs, with Kaylie complaining loudly and firmly that she wasn't tired and didn't want to go to bed. Her mother was just as firm (though not so loud) that it was late, it was already past her bedtime, and she was going to go to bed.
The mother tucked Kaylie into bed, ignoring her continuing protests of being wide awake. She did agree to reading a bedtime story, about a young Hispanic girl who had an apparently magical backpack, a monkey for a companion, and friends who were willing to drop whatever they were doing to help her.
The boggart meanwhile was probing the girl's mind, trying to find out what would frighten her most. This was harder than usual, because the little girl didn't seem to fear very much. True, there was sort of a generalized fear of the dark, which most kids seemed to have, but that didn't do any good. How could a shape-shifter turn itself into "the dark"?
It finally found what it was looking for in an old memory from when the girl was barely two. A big black and brown dog had growled and barked at her, more as a warning to stay away than any real threat. But she'd been so little and the dog so big that it had terrified her. Even though she was older now and didn't normally have any fear of dogs in general, she still had an ancient and deep-seated fear of this dog in particular.
When mother reached the end of the book, and the girl in the story had successfully accomplished whatever it was she'd set out to do, she tucked Kaylie in, kissed her good night, and left the room, turning out all the lights except a small night light next to Kaylie's bed. The little girl rolled over facing the door, cuddled up with her stuffed rabbit and closed her eyes.
The boggart was ready now. It floated out from under the bed, transforming into the big black and brown dog and growled. Kaylie's eyes flew open and she tried to scream, but she was so scared no sound would come. Terrified, she grabbed the blanket and pulled it over her head.
The Muggle word for boggart is bogeyman. And everyone knows you're safe from the bogeyman if you're under a blanket.
The boggart was confused. The little girl had disappeared, and it had no one to scare anymore. It dissolved into mist again, and drifted back under the bed.
Minutes later, Kaylie peeked out from under the blanket. She was alone again; there was no big dog in her room, or anything else scary. She cuddled her rabbit tightly, and settled back down again, still unsettled but calming down.
The boggart sensed her again as soon as she came out from under the blanket. It drifted back out and again assumed the dog shape. Kaylie watched it emerge, and dove back under the blanket again. The boggart again went back to mist, and retreated under the bed.
Kaylie stayed hidden longer this time. She peeked out without lifting the blanket off her head, ready to jerk it back over her head at need. With only her eyes exposed, the boggart had no idea she was still there, so it just floated under the bed, thinking boggart thoughts.
She waited a long time, almost half an hour, before taking the blanket off her head and lying down again. Her hands clutched at the blanket, just in case, the rabbit forgotten.
As soon as she was out from under, the boggart slipped out and assumed the shape of the dog. This time, Kaylie screeched and threw the blanket over the boggart as she leaped out of bed and ran for the door.
Boggarts can be fooled when their victims hide under the blanket. But when the boggart finds itself under a blanket, it becomes terribly, terribly confused, uncertain whether it even exists or not. The boggart froze for a moment, then dissipated with a crack and disappeared from the house.
Wizards can use Ridikkulous and a good laugh to banish a boggart. But Muggles can do the same thing using just a blanket.
Kaylie's mother brought her back into the room and showed her there was nothing under the blanket, and nothing under the bed. Kaylie insisted on having the room light on while she went to sleep, and her mother allowed it. With the blanket back in place and the rabbit clutched tightly, Kaylie dropped off to sleep.
And was never bothered by a bogeyman ever again.