Revealing mistake: When Sassy comes out of the burning house carrying the kitten in her mouth you can tell that the kitten is fake.
Revealing mistake: When Kevin shows the Mayor the Times editorial about the judge he quotes a phrase from the article about whether the man would be a judge if not a former law partner of the mayor. Unlike many newspaper articles shown in films where if you read the article text it is actually jibberish, here it is a legitimate article criticizing the way judges are elected, but some parts are repeated, and it states nothing about the judge being a former law partner of the mayor.
Revealing mistake: After Seagal and the student jump off the window they land on the floor and for a brief but obvious moment one can notice it's not Seagal but his stunt double.
Revealing mistake: When "Roy" pushes Martin into the wall during their first meeting, you can see the wall shaking on impact. (01:14:30)
Revealing mistake: At the start of the montage in which Frollo ransacks Paris for the gypsy girl, the shot of the three soldiers kicking down the baker's door very briefly places the more distant soldier off to the right "in front" of the closer central soldier; this is a case of incorrect animation cel layering.
Revealing mistake: During the scene with Patricia Arquette sitting on the hotel toilet in her robe, she reaches for the toilet paper and spreads her legs for a moment. We can see she is wearing panties while she was supposedly doing her business.
Revealing mistake: When the Leprechaun gets sucked into space, he grabs onto the edges of the cargo bay's doors. You can see pieces of his hands disappear into the doors, showing that it's CG.
Revealing mistake: Looks like Frosty Cream is actually a Dairy Queen. When Karl is ordering, the menu board behind the employee lists items such as "DQ Sandwich", "Dilly Bar", and a spot where you see part of DQ's old motto.
Revealing mistake: When Kiki's legs "reverse" at the end of the film as he runs off, watch closely. It is clear the effect was achieved through some shoddy image-manipulation. His clothing and hands "warp" slightly a few times around his legs.
Revealing mistake: When Diana is about to jump off the plane onto the galloping horse, her hair moves wildly. When the shot changes, she has been replaced by a stunt who looks nothing like her and has her hair fixed.
Revealing mistake: When the policeman is shot on the roof of the observatory and the police cars drive across the grass, you can see the tyre marks in the grass from previous takes.