- During the sea storm, the rogue waves morph into a giant demonic entity made of sea foam and water - Father Neptune on acid.
- The Giant Mouse of Minsk is unsettling by design — it was made to scare off the cats, after all — and even though it's our heroes' weapon to win the day, it's terrifying. The head and other parts of the Mouse are rotoscoped (traced over live footage: the producers made and filmed an actual Mouse) giving its movements an eerie realism and making it seem unworldly.
- The Giant Mouse of Minsk was the closest thing that the immigrants could come up with to a tank - from the cats' perspective, it's a huge, armored juggernaut spitting missiles (well, fireworks) at them! It's little wonder they ran for the hills!
- The Russian cats in the beginning of the movie chasing after Fievel and the fact they were like monsters (in Fievel's point of view.) They sound like like big cats rather than small cats, too. Same thing with the cats in New York.
- The humans at the beginning, who the cats were imitating. The movie started out with a pogrom.
- There's a whole lot of Adult Fear too if you put yourself in Papa's position.
- And for Papa himself, too. In "There Are No Cats In America," Papa starts off the song by mentioning that he and his family were just walking to Minsk one day when he was young, then they saw evidence of a cat in the area, Papa faints, and he wakes up to find his entire family had been killed and eaten. That's a terrifying prospect for any parent, one that transcends their own death: now, their child is all alone in a world where they're at the bottom of the food chain...
- The Not So Different aspect of America vs. Europe with regards to the cats' oppression of the mice (representing the oppressed, disenfranchised lower classes of the world). Not only is it made abundantly clear that, yes, there really are cats in America, the scene demonstrating this is quite horrific. It starts with Fievel very nearly being eaten, whole and alive, by a cat and only surviving thanks to Cartoon Physics. Some other mice in the scene aren't so lucky: a few are grabbed by other cats with the clear implication that they're about to be Eaten Alive even though it cuts away to other shots of the cats terrorizing the mice. To hammer home that the mice are no safer in America than they were in Europe, the scene reuses animation cels from the Cossack raid on the Russia village earlier in the movie.
- If you were even remotely afraid of insects the swarm of roaches in the sewer were pretty creepy...
- Imagine them if you're Fievel's size, and the roaches are bigger than you are...*shudder*
- And that hideous fish that was eating the roaches! It appears only once and is never mentioned again.
- One instance in Fievel Goes West was the hawk and scorpion scene. AAAAAAAAHHHHHHHH!
- The part where the scorpion almost stings Fievel right between the legs will make anyone cringe.
- THE LAAAAAAAAAAZY EYE.
- Some of the monsters Fievel imagines in Mystery of the Night Monster, like the one from the first scene.
Nightmare Fuel / An American Tail