"100 Mile Walk": Charles is forced to make a pilgrimage to a far-off work site due to being strapped for cash, as well as a neighbor, Jack, both trying to support their families. There is Foreshadowing in the middle of the episode that the place Charles, Jack, and company on the job are working is full of dangerous explosives that never went off, like a forgotten minefield. After they finish the job, Jack gets so caught up with excitement he carelessly runs around the place celebrating in glee... only to accidentally set off one of the charges that failed to detonate and get vaporized by the resulting explosion- and we are not treated to a Gory Discretion Shot. The moment he steps on the wrong place at the wrong time, there's a very violent and abrupt BOOM, and Jack is literally blown sky-high, with a panning shot of the resulting smoke cloud rising up into the wild blue yonder, helping to illustrate the fact he got blown to kingdom come. And this is just the fourth story.You know, for kids!
"Plague": Seeing all the rats running around the storeroom where the cornmeal is stored can be very unnerving. Not helping: An eerie musical cue is played. Worst of all is when Doc Baker demands, "Burn this place to the ground." That's exactly what the townsfolk do while the rats are still inside, and all those rats are implied to be immolated to kill off the plague carriers.
"May We Make Them Proud": It can be chilling, downright frightening to watch the scene where Alice Garvey is trapped in the burning house and beating her arms on the window to try to break it and escape screams for help. Then the flames swallow her and the crying baby, Adam Kendall Jr., she is holding. Also, hearing the baby stop crying as he and Alice are overcome by the flames and intense heat indeed, there is a cut scene of a huge fireball shooting out the window of the room where they were just standing is horrifying. This, despite the fact that the scenes of Alice crying for help were shot on a soundstage, Heresha Parady (Alice's portrayer) was holding a doll and the baby crying was just sound effects perfectly stopped on cue and added in post-production.
"Sylvia": The evil clown mask that the rapist hides his face behind. The fact that the rapist stalks his victims — in this case, Sylvia — is also enough to give the viewer shivers. It is also scary to see the climatic scene, where Sylvia is once again visited by her rapist and, attempting to climb a rickety ladder to escape, plummets to her death.
"Home Again": Michael Landon does not pull any punches when showing Albert withdrawing from morphine. They are as graphic as one will ever see, and as such this was a rare episode in an episode where most everything else was as G-rated as possible where parents were urged to watch with their children.
"The Music Box" is both an in-universe example and an example of something that could shake up young viewers. After stealing the eponymous music box from Nellie's room, Laura suffers guilt that manifests itself as three nightmares, one in a courtroom, one in a jail, and one where she is being hanged. All three show Laura in a ragged dress with tangled, dirty hair and shackles on her wrists. All three also have a sadistic minor version of the music box tune as background music. The jail nightmare also features a grim-faced matron throwing scraps at prisoners, who then throw themselves on the floor and gobble them, groaning the whole time.
The episode "The Monster on Walnut Grove" has a few scary scenes, both of Laura's nightmares are really nightmare fuel. In her first nightmare, Nels is shown chopping off his wife's head and then Nellie's, Willie's and Laura's heads are flying around screaming.
Albert's sickness in "Look Back to Yesterday", especially when he cheerfully speaks without knowing a huge geyser of blood is pouring out of his nose.
The final destruction of Walnut Grove in "The Last Farewell" isn't pretty to look at. All those iconic building are shredded to bits in very loud and shocking explosions that are shot in slow-motion film just to make it sink in.
"Whisper Country" was a really creepy episode, as the overly religious people made the show creepy and treated Mary like an evil outcast. Miss Peel was really a creepy character in the episode and accused Mary of being a "jezebel."
Little House In The Big Woods makes mentions of panthers. One that chased Laura's Grandpa home in a story, one that was stalking her Aunt Eliza (her dog Prince intervened), then in Little House on the Prairie it provides Pa and some Native American tribesmen the the incentive to hunt and kill it.
Ma and Laura's encounter with the bear in the cow pen.
Farmer Boy usually isn't the most exciting book but has a few nightmarish moments.
While helping with ice cutting, Almanzo slips on the ice and starts sliding towards the open water. He's saved by one of his father's workmen, but he describes in graphic detail how he "knew he would sink and be drawn under the solid ice. The swift current would pull him under the ice, where nobody could find him. Hed drown, held down by the ice in the dark."
Later, while helping harvest potatoes, Almanzo takes a break to cook two of them for his sister and him to eat. He builds a fire and begins roasting them, only for one of them to explode and hit him directly in the eyes. He's not seriously injured, but it's about the last thing you expect to happen in that scene.
Little House on the Prairie is full of Nightmare Fuel, just owing the hardships of being a homesteader:
Pa nearly drowns trying to ford the wagon (which holds Ma and the girls) across a swollen river. Pa gets in the water with the horses while Ma tries to steer; the terror in her voice as she tells Laura and Mary to lie down and lie still is palpable even though it's told by 4-5-year-old Laura.
While building the cabin, a log rolls off from a height and falls on Ma's foot. Her ankle is sprained and swollen, and it's explained in the narration that a small divot in the ground was the only thing to save the foot from being completely crushed.
The "candle in the well" portion of the book comes off as a simple cautionary tale. Pa even improvises a science experiment for Laura out of it. Never mind the neighbor helping Pa build the well nearly dies after passing out due to toxic underground fumes.
Laura is awoken in the middle of the night by wolf howls. Pa lifts her up to look out the window, where a pack of them have surrounded their cabin on all sides. The cabin that was recently built and has no door or window panes.
Pa is caught up in a pack of wolves while out hunting. He described them surrounding his horse and just trotting alongside, unafraid (though Pa, understandably, was terrified). Pa comes back shaken, having had to control the horse's natural instinct to run so as not to spook the wolves.
The entire family comes down with malaria and it's only the fact that neighbors find them and seek medical help that they survive.
Interestingly, Baby Carrie isn't mentioned in the malaria scenes at all, which makes sense, because while Carrie exists in the narrative, she wasn't actually born yet; the books being a somewhat fictionalized account of Laura's life. So while some readers might get some Fridge Horror regarding who exactly was taking care of the baby while the family was bedridden and hallucinating, it's good to know she wasn't actually in danger. However, that brings up some Real LifeFridge Horror regarding the incident. Dr. Tan, the doctor who treated the family, is noted on his gravestone as having done so in 1870. Little House on the Prairie puts these events solidly in the summer, when the weather is hot and the mosquitoes are out. Carrie was born on August 3, 1870. Put this information together and what do you get? The horrifying realization that Ma was heavily pregnant with Carrie while nearly dying of malaria on the high prairie. Since real-life Carrie was small and frail throughout childhood, it's possible this might have been part of the reason why.
Laura's fever dreams while sick with malaria are pretty trippy.
Pretty much anything involving the grasshoppers in Plum Creek, including Laura being outside when the glittering cloud appears, and grasshoppers start plunking down on her head, the ground being carpeted with grasshoppers, to the point the family can't walk to church, the creek being plugged with drowned grasshoppers, and, of course, grasshoppers climbing in through the open windows, and walking right over baby Carrie.
A lot of The Long Winter, in-universe and out. Laura starts having nightmares that the blizzards are deliberately trying to scour away the roof to get to them. Quite a lot is made of the fact that the blizzards always seem to come out of nowhere, so there's always a risk of getting trapped away from home and freezing to death.
Honorable mention to the snowstorm that catches Laura at school. The entire school must walk in blinding snow to get back to a town they can no longer see ahead of them. It quickly becomes a nightmarish slog as Laura realizes that they've been walking far too long, shortly before she bumps her shoulder against the final house on the street and calls everyone back. If they had continued to walk, the entire school would have been lost on the open prairie.
Also the description of each of the malnourished family members' thin bodies and hollow cheeks, and hunger-induced apathy, where "only the storm seemed real." Garth Williams' charcoal illustration show an image of Pa visiting the Wilder boys in which the man's face is noticeably gaunt and hollow-eyed under his full beard, and in future books Carrie is said to be noticeably thin, frail, and prone to fainting due to her harrowing starvation.
A blizzard nearly kills some cattle. How? Their breath freezes their heads to the ground, and they come close suffocating. This phenomenon is addressed again in These Happy Golden Years, when Almanzo, who is driving Laura home from her teaching job for the weekend, has to keep stopping to melt the ice on his horses' noses.
From Little Town on the Prairie: The hideous needle-grass that screws itself through Mary's stocking, followed by Pa's description of cows eating said grass, forcing it to be cut from their lips and tongues.
Laura wakes up in the middle of the night to Pa yelling and a soft "thud." A mouse had been chewing on Pa's hair while he slept and in a sleep-induced panic, he grabbed it and threw it against the wall. This is framed as a funny anecdote leading to the purchase of a kitten to become a mouser.
Later, the kitten, technically too young to leave its mother, gets into a fight with a mouse and nobody intervenes, despite the mouse being as large as the kitten. The fight and ensuing kitten injuries are described in detail and with pride, as the kitten wins the fight.
Laura's time at the Brewsters in These Happy Golden Years. Laura is forced to board in a house thirty miles from the nearest neighbor with a woman slowly going insane from isolation...and she doesn't like Laura. And she has a knife. It's easily one of the darkest moments in the series, particularly when the woman's openly threatening suicide, if not murder-suicide: "If I can't go home one way, I can another."
When Almanzo picks Laura up and drives her home for the weekend, he has to remind her to stay awake, lest she die of hypothermia.
After a cyclone, Pa comes home with a story of two brothers who were traveling home with their mule when the storm hit. One of the boys was picked up by the cyclone, which somehow stripped off every piece of his clothing down to his high laced boots before slamming him to the ground, where he ran home otherwise unharmed. His brother and the mule are found days later with the grim sentence "Every bone in their bodies was broken."
A couple of Adult Fear moments in The First Four Years: When the horses jump over baby Rose. And when Boast tries to buy Rose in exchange for his best horse.
Laura's first childbirth is likewise a little out there. From a medical standpoint, the fact that the doctor gives her chloroform (now known to be very toxic) is pretty horrifying, too.