The darkly humourous Lamb to the Slaughter, about a woman who kills her husband with a frozen leg of lamb. Guess how she disposes of the murder weapon. Come on, guess.
You were wrong. She feeds it to the police.
"The Landlady" takes place in Bath at a bed and breakfast with an unusually friendly landlady. Later Bill, one of the guests, recognizes the names of two others; we find out that they checked in 2 years ago but never came out. She also has realistic stuffed animals... because they're her old pets. She freely admits to stuffing them herself. Upon which Bill notices that the tea she gave him had a smell and taste of Bitter Almonds. Then she asks if he signed his name to the guestbook, so she can remember it...
Man From the South. Not so much Nightmare Fuel as a distressing insight on how easily people will submit themselves to bodily mutilation if the reward is good enough.
They made a TV episode out of this for the original Alfred Hitchcock Presents, directed by the master himself. The guy making the bet? Peter Lorre. There is also a version from the 1985 revival of the series, with John Huston in Lorre's role.
Royal Jelly. A story about a man with a natural affinity for bees who decides to give his sick baby royal jelly to cure her. Except it works too well, and the baby begins to look more like a puffy larva. And the man had been taking royal jelly for months before hand, and is beginning to look more and more like a bee...
Pig: A rural guy who's been living on a farm all his life with his chef aunt, goes to NYC and into a restaurant where the chef serves him the special, pork and beans... The chef invites him to a factory tour where he ends up on the conveyor belt, being turned into a pig and is then sliced apart. See the title picture of Charlie and the Chocolate Parody.
Your imagination just runs wild after reading Skin, eh? It ends with almost no explanation. Just that the old man's tattoo is being displayed in a museum. And there's no Bristol Hotel in Cannes...
Beware of the Dog: The short story told from the perspective of the downed British fighter pilot who's in Occupied France the whole time.
Genesis and Catastrophe: a couple who already lost several children before are about to have birth again. Her mother worries about the fate of their new child and notices he's very frail. The story ends with Klara praying, "He must live, Alois. He must, he must... Oh God, be merciful unto him now..." Then the audience learns the boy's name: Adolf Hitler!
A real mindfuck is William and Mary, about a man who dies, but in his will he explains to his wife that he took part in a scientific experiment in which his brain is being transplanted from his body after death, and attached to an artificial heart. The brain would be bathing in a Ringer's solution. One of his eyes could also be hooked up so that he would be able to see. Although the doctor is uncertain whether the brain would regain consciousness, he remains hopeful. The brain, he says, could probably live as long as 200 years connected to the machine. If that isn't horrible enough Mary turns out to hate her husband and enjoys having her revenge on him by taking him home and do everything he always prohibited her from doing, while he just lies there in this helpless state!
The Witches: Easily Dahl's most frightening children's book.
The Grand High Witch ... once she takes off her mask. In the movie it's just as scary. And when she starts "frying" one of the witches: it's just as awful. Later Grandma informs her grandson that the Grand High Witch fries at least one witch each meeting!
The chapter where Grandma tells about all the children she knew who became victims of witches.
The story about the little girl who was transformed onto a painting in the house of her parents and family. It's worse enough that your child disappears and yet can be seen on a Spooky Painting every day, but apparently her image on the painting changes every day: she even gets older... until she finally disappears entirely!
Each anecdote is frightening in itself, but then it turns out she herself was once a victim. She refuses to tell what happened to her, but then her grandson asks "Did it have something to with your missing thumb?". This causes Grandma to freeze in shock, thus abruptly breaking off the conversation. The boy then decides to go to bed, wishes her goodnight and the last image he sees of her before going to his room is that she is still sitting in her chair shaking and unable to register what's happening around her. In the next chapter grandma and son are back on speaking terms, but how she exactly lost her thumb remains Shrouded in Myth, causing many young readers' imaginations to go berserk!
The boy protagonist playing in his tree house until a strange lady (clearly a witch) tries to talk him to climb down and talk to her. He recognizes what she is immediately and refuses to do so, remaining up the tree, long after the witch finally leaves and evening sets in...! Then finally his grandmother comes looking for him.
This book is filled with nightmare fuel, but the worst was when you are told that American witches particularly like turning children into food and getting their parents to eat them.
Quentin Blake's illustrations to the story are equally terrifying. Some of those witches are just... stuff to lie awake about at night.
The Wonderful Story of Henry Sugar and Six More includes "The Swan", in which a little boy is bullied by two larger boys with guns. One of their first acts is to tie him to a train track, thinking that'll kill him. The boy survives, but the story details his feelings and fears as the train rushes over him. The last act of bullying includes cutting the wings off a dead swan, strapping them to the boy's arms, making him climb a tree, telling him to "fly," and then shooting him in the leg when he refuses to jump off.
It's not so scary when you realize that he does fly away. The final paragraphs of the story have him crashing sobbing and bloody through the door of his family house, where his Dad promptly calls the authorities...before cutting the severed wings from the harnesses on his son's arms.
Not to mention the title story itself, in which the idle, wealthy, selfish Henry learns about, and subsequently trains himself to have, the ability to "see without eyes" — specifically so he can see through the backs of cards and clean up at casinos. Dahl viciously describes a sequence in which Henry, feeling "a strange pain in his chest", applies the ability to his image in a mirror and sees a blood clot slowly making its inexorable way to his heart, unstoppable and deadly...Then he reveals that it was only a potential scenario that didn't actually happen (the story uses a Direct Line to the Author setup), but would have been appropriate since it would have directly referenced the heavy implication that Henry's predecessor suffered a Karmic Death as a direct result of using his powers for personal gain — more Nightmare Fuel! In fact, what "actually" happens is that Henry's greed lessens in the wake of the training. He subsequently becomes a sort of Robin Hood, cheating casinos all over the world under a variety of disguises and aliases to fund a chain of orphanages — the "Wonderful" part of the story.
What makes this all the better was that, in the UK at least, The Wonderful Story Of Henry Sugar collection was calmly pitched as a short-story collection for children. Older children, admittedly, but still. (In America, it can be found in elementary school libraries.)
The non-friendly giants in The BFG. Especially in the film version, which gives the giants blue skin, horrible voices and slobbery jaws. They were pretty much designed to cause nightmares and lack of sleep in children, particularly because they prey on children while they sleep in their beds.
The Trunchbull from Matilda - a massive, super-strong, psychotic woman with a horrifically violent temper and an incredible hatred for children, who just so happens to be headmistress of a primary school. Her punishments only add fuel to the fire - lobbing children out of windows, slinging them around by their hair, force feeding them cake, and, worst of all, locking them in a tiny cupboard in her office called the Chokey, which has broken glass and nails sticking out of the walls. The absolute worst part about her though? The children have tried to tell their parents about her before, but what she does is so outrageous that their parents don't believe them!
Crocky-wock the Crocodile who sneaks inside a father and son's house. They hear him downstairs, but are unable to do something in time. So the creature crawls upstairs, enters the room and presumably eats them.
The Ant Eater devouring both the spoiled boy and his aunt. Even though they deserved it...
The tummy monster. Especially since you have no idea how this creature got inside the fat boy's tummy and how it looks.
The original illustrations by Rosemary Fawcett were pretty frightening as well.
The ending, where Mr. and Mrs. Twit are glued to the ground while standing upside down on their heads. Their fate is disturbing enough, but Dahl adds that due to the pressure of their bodies pushing on their heads they are actually pressed together! Their heads disappear inside their bodies and their bodies inside their legs until nothing more is left than their clothes.
Dahl's descriptions of some of the misadventures he actually suffered as a child in the memoir Boy, including almost losing his nose in a car accident and having his tonsils removed without anethstetic, are enough to make your skin crawl. The description of the horrid old woman who ran the local sweet shop, digging her filth-encrusted fingernails into a jar of toffee, is also the stuff of nightmares.
George's Marvelous Medicine is in many ways more lighthearted than many of his others, but the effects of the medicine are described in a detail that gets rather gruesome. However, one scene that is even more scary precisely because it's so mundane is the part where the grandmother scares George by talking about Nausea Fuel things she's eaten and makes him think she might be an actual witch. There is every indication that she's lying about any magic powers she might have or the vile insects she has eaten... meaning that she's simply a cruel old bitch deliberately terrorising her grandson while his parents are out, in such a way that even if he told them about it she could all too easily use the "Just Joking" Justification or downplay it. This scene taps into both the childhood fear of being helpless in the face of cruelty without the support of your parents (a main reason for why Miss Trunchbull is so scary,) with the addition of it happening in your own home, and the Adult Fear of knowing that your own child could go through something similar, and that you yourself might not treat it seriously because it would inevitably get softened in the retelling.