Continuity mistake: When Ronald is in the store talking to Cindy about renting her and the salesman is looking at them through the telescope, Ronald has the money in his hand fanned out. When the camera cuts to the store, the money is not fanned out in his hand anymore.
Other mistake: At the shop where Cheech works, you can see him lip synching the redhead's lines as she says them.
Continuity mistake: In the part where the nerds are in jail, there is a close-up scene of a mean character that throws down his playing cards before he approaches them, but then when the next (wider) angle is shown, you can see the same man throw down his cards again. (00:57:55)
Audio problem: In the mansion, the boys open a secret passage and fall through the floor. They scream after shining a flashlight on a skeleton. Eugene then can be heard whining that he wants to go home, but his mouth is not moving.
Continuity mistake: When Lynda is running out of the garden gate after an argument with her father, she throws the rake behind her. In the next scene, when her father steps on it, it is in a completely different position.
Visible crew/equipment: When Jesse is in the kitchen trying to get the skull from the bird's mouth, you can briefly see the puppeteer operating the bird in the lower right corner of the screen.
Revealing mistake: When Ali Gator and Windy Winston are coming back from the barfight riding the atv's, Ali scratches his head and you can see where the green glove ends and the actors real skin is supposed to be, under the shirt.
Revealing mistake: Toward the end, after Ricky decapitates the old Mother Superior, a young nun assumes she is alive and taps her shoulder. Mother Superior's head falls off and to the floor. There is no blood whatsoever. The old woman had just been decapitated moments earlier, and there isn't even a drop of blood, not even on the white part of her nun outfit at the neck.
Visible crew/equipment: The boom mic is visible when Sally sings her "Pie in the Sky" song and when Courtney and Sally are standing in the bathroom, before Sally's face explodes.
Continuity mistake: When the chimp, Goofy, is flying using the simulator, he's flying haphazardly and crashes into a red truck. He then turns and smiles at the trainer. In the next shot, he is flying haphazardly again.
Revealing mistake: At the end when Whoopi falls down the hill and hits her head on the rock, it's obvious that the rock is not real, since the rock moves very easily considering its size.
Continuity mistake: After Todd Howard knocks out his opponent in the boxing match, the crowd immediately starts throwing cups of popcorn into the ring. The camera cuts to Todd cheering and then an overview shot of his opponent laying face down on the canvas. At that view you can see that there is no rubbish or popcorn or anything else in the ring. Then when the camera cuts back to a side view there is loads of rubbish and popcorn all over the place once again.
Continuity mistake: When the angel lands face down in the pool, Michael Knight turns her over and her face is completely dry.
Continuity mistake: During the scene when Bobby's auditioning for a part, there's a picture on the wall of Helen Martin (the lady playing Bobby's Grandma). The picture disappears and reappears during the scene.
Continuity mistake: When the pirates swears the oath to kill Dragon Mao, they drip blood on one of the pirate's hand. The blood stains on his hand differ between the shots. (00:02:50)
Plot hole: The fact that Buddy placed the knife and note in the steering wheel of Jerry's car is unrealistic. Buddy first met Jerry in the bathroom after school started and Jerry hasn't gone outside of the school building to his car until this point later in the morning... so there's no way that Buddy could have known which car was Jerry's to pull this stunt.
Continuity mistake: When George's wife asks him what made him drive all the way out here, their car is on the back of a large dinosaur at that moment. When it cuts to a closer angle for his reply, suddenly they are on a dirt road.
Continuity mistake: When Molly Ringwald is on the phone at the club and gets approached by the girl in orange, throughout the whole conversation the position of the phone receiver in Randy's hand is wildly inconsistent. (00:09:30 - 00:11:00)
Character mistake: When Modoc is suggesting what type of blood to drink, he suggests pigs blood B-. Swine don't have B blood. They have A and O blood only.
Revealing mistake: There are times in the movie when you can tell Bobo's beard is fake such as when Penny's giving him a drink from a 7-11 and it's peeling off near his right ear.