Continuity mistake: When Rand is showing the old man his invention, he pulls the toothbrush up, and it is facing away from him. When the shot changes the toothbrush is now facing him. (00:02:30)
Continuity mistake: After Rand squirts the toothpaste all over his jacket, it all completely disappears after he gives the shop owner his card. (00:02:45)
Continuity mistake: This is in the scene near the beginning of the movie at the bar where Billy's girlfriend works. Billy is sitting at a table drawing. He is joined by the Vice President of the bank he works at. He sits down and starts talking to Billy. Billy looks up at him while he's talking. Then in the next shot, which shows them both, Billy is looking down at his drawing as if he weren't even paying attention. (00:14:10)
Continuity mistake: When Billy puts the santa hat on Gizmo, in the first shot the hat is folded backwards so that the bobbled end is hanging behind the hat. In the next shot it hangs over the front of the hat. (00:19:45)
Continuity mistake: When Pete is laying on Billy's bed talking to Gizmo, in one shot he's laying on his stomach, then in the next shot he's laying on his side. (00:23:55)
Continuity mistake: When Billy accidently squirts shaving foam onto his father, by use of the bathroom buddy, the foam around Rand's mouth disappears between shots. Foam also appears on his glasses between shots then disappears too. (00:27:15)
Continuity mistake: When Dr. Hanson dismisses his students, a box falls, produces smoke, and he moves backwards. From a different angle the smoke is gone and he is repeating all the movements. (00:46:05)
Continuity mistake: In the dark classroom, Billy grabs for the phone, but the Gremlin grabs him. Billy then backs away. We then see the Gremlin reach for an apple which is sitting next to the phone. But the apple wasn't there in the previous shot. (00:47:40)
Continuity mistake: Soon after the Gremlins hatch from their cocoons, Billy goes to the school to check on the professor. When he walks into the classroom, he leaves the door open. Later, when he leaves the classroom, he has to open the door again. (00:49:20 - 00:50:30)
Continuity mistake: When Billy's mom grinds the Gremlin in the food processor, the fridge to the left swaps from dirty to clean. (00:54:35)
Continuity mistake: In the kitchen, Billy's mom shields her face with a table. A frame later it's at waist level. (00:54:50)
Continuity mistake: Right after the mom sprays the Gremlin in the face with the flea and tick spray, forcing him into the microwave, we see the Gremlin cooking away in the microwave with the spray can in the foreground, its label facing the camera. In the shot where the Gremlin blows up, the can's label is no longer facing the camera, plus immediately after the Gremlin goes ka-blooie, something cracks in front of the spray can, distorting our view of it. (00:55:30)
Continuity mistake: Watch Billy after he has been first attacked by Stripe by a clawing to Billy's chest. He is wearing a sweater with a white T-shirt underneath. From that moment on the torn area of his sweater and the blood marking on the white T-shirt continuously change shape and size. And if Stripe's claws were sharp enough to cut him that badly, how come it didn't cut through his white t-shirt under his sweater? Because Billy showed a lot of pain when he was clawed. (01:01:55)
Continuity mistake: Before Mrs. Deagle is attacked a portrait appears on her table between shots. (01:08:25)
Continuity mistake: When Billy turns to Kate, because she says "Now I have another reason to hate Christmas", he is holding a flashlight up by his chest, yet when the shot changes he is holding it down much lower. (01:15:45)
Continuity mistake: Kate has a bruise on her right cheek near the end. When Billy tells her all the Gremlins are in the theatre and she says "All of them," her bruise is on her left cheek for the one shot. (01:19:25)
Continuity mistake: When Billy smashes the Candy store window the amount of stuff behind the glass changes between shots. (01:27:50)
Continuity mistake: A pair of baseballs and several cans appear behind Billy when Stripe attacks him with a chainsaw. (01:32:35)
Continuity mistake: When the movie ends, the sling around Billy's neck is either over the collar or under, depending on the shot. (01:38:35)
Continuity mistake: When the old man is leaving the family's home, in the indoors shot as he turns to walk out the front door, he is holding Gizmo's box under his right arm, and has the "smokeless ashtray" in his left hand. Cut to the outside shot of him walking through the door, and he is suddenly holding the Mogwai box by it's handle, and has nothing in his left hand. (01:42:00)
Answer: The original film was released before the PG-13 rating existed (it was one of the films responsible for its creation). Producers decided to remove some of the language and violence for the DVD release to avoid complaints about the PG rating.