There was nothing here that frightened her. These things – even the thing in the cellar – were illusions, things made by the other mother in a ghastly parody of the real people and real things on the other end of the corridor. She could not truly make anything, decided Coraline. She could only twist and copy and distort things that already existed. (10.9)
This passage implies that the other world isn't a reality, it's just a "ghastly parody" (a scary imitation) of the real world.
The other mother was huge – her head almost brushed the ceiling – and very pale, the color of a spider's belly. Her hair writhed and twined above her head, and her teeth were sharp as knives […]. (11.7)
The other mother turns into a monster here, which we're guessing is her true form. She was never really a copy of Coraline's mother at all. Also, check out the "Character Analysis" for the other mother for more on her similarities to a spider.
The wall she was touching felt warm and yielding now, and, she realized, it felt as if it were covered in a fine downy fur. (11.48)
As Coraline starts to escape the other world, it's like the entire place falls apart and morphs into some sort of strange being. It actually made us wonder if the other mother and the other world were the same sort of creature.
The picture they had in their own hallway showed a boy in old-fashioned clothes staring at some bubbles. but now the expression on his face was different – he was looking at the bubbles as if he was planning to do something very nasty indeed to them. (3.41)
This is a great detail, and it really helps to set the tone for the entire other world.
The house looked exactly the same from the outside. Or almost exactly the same: around Miss Spink and Miss Forcible's door were blue and red lightbulbs that flashed on and off spelling out words, the lights chasing each other around the door. (4.1)
This description makes the other world seem sort of fun, and images like this emphasize how Coraline could have been fooled by the other world. The other mother did a decent job of making it look cool, at first.
"I suppose. But if you're the same cat I saw at home, how can you talk?" (4.9)
Among the weird things in the other world is the fact that animals can talk. This difference turns out to be really important for Coraline, since it helps her find her only friend.
And then it took shape in the mist: a dark house, which loomed at them out of the formless whiteness.
"But that's –" said Coraline.
"The house you just left," agreed the cat. "Precisely." (6.51-53)
The fact that the entire other world is so small makes Coraline feel disoriented; imagine if suddenly all that existed was your house and your yard.
There was nothing else there in the mirror. Just her, in the corridor.
A hand touched her shoulder, and she looked up. The other mother stared down at Coraline with big black button eyes. (6.74-75)
This scene freaked us out a little and made us wonder if the other mother was a vampire. We love the immediate shift here, too. One second, Coraline is alone, the next, the other mother is there.
Through the stone the world was gray and colorless, like a pencil drawing. (8.116)
Once Coraline starts looking through the stone, we see a sharper contrast between what the other mother wants her to see, and what the other world really is. Which one – if either – is reality?
She got to her front door – now just a small child's scrawl of a door – and she pushed her hand against it, half expecting that her hand would rip through it, revealing nothing behind it but blackness and a scattering of stars. (10.63)
Everything in the other world is so foreign to Coraline that it almost feels like she's in outer space.