One example in particular would be Zelda, especially the second scene she's in.
Also, the story Jud tells of Bill Baterman, who buried his son in the burial ground, and everything that followed. Doubles as Nausea Fuel in places.
King waited a year after finishing this manuscript before submitting it to the publisher because he was so horrified by what he had written. Stephen King scared himself with this story.
"Mommy, I brought you something!"
From the movie: "I'm at Jud's, Daddy. Will you come over and play with me? First I played with Jud. Then Mommy came and I played with Mommy. We played, Daddy. We had a awful good time. Now I wanna play with you."
Pascow losing his brains on the carpet...then coming back to haunt Lewis.
A more prosaic example, when Louis mulls over resurrecting Gage.
Do you want to resurrect a zombie from a B-grade horror picture? Or even something so prosaic as a retarded little boy? A boy who eats with his fingers and stares blankly at images on the TV screen and will never learn to write his own name? What did Jud say about his dog? "It was like washing a piece of meat." Is that what you want? A piece of breathing meat?...Did he believe it would be impossible for him to love Gage even if Gage had to go on wearing diapers until he was eight? If he did not master the first-grade primer until he was twelve? If he never mastered it at all?
The bit where Louis is walking through the swamp, alone, at night, and there is something else just out of sight.
Pet Sematary: Especially the scenes involving Zelda's drawn-out death and Gage being hit by the truck. What's interesting about the Gage scene is that it was based on a real-life incident involving King's young son. Fortunately, King's son didn't get squished by a truck and fell over before he could get to the road. The cat getting hit is also creepy/sad, and based on another true incident. The real-life cat also died.
Louis' second trip through the swamp and up to the burying ground. He feels a presence behind him, and he describes how he imagines it to look, but that doesn't make it there. And that freaky, bifurcated-horned face thing. shudder
Any scene of the film featuring Zelda was terrifying beyond words. The fact that Zelda was played by a deformed-looking man might be part of what makes her appearance so traumatic.
In Jud's flashback to the story of Timmy Baterman, after Timmy is resurrected. At one point, he's squatting in the yard and holding what looks like a small girl's leg. Now, that might be a doll's leg, but it looks pretty bloody at the stump.