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: 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: 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: 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 Billy discovers Barney the dog wrapped up and hanging by the Christmas lights, Barney's face is pointed towards the house, but when the shot changes to Billy helping Barney down, the dog's face is turned away from the house.
Continuity mistake: When the gremlins are attacking Billy's mom in the kitchen, the kitchen is well lit with a window that allows sunlight into the room, but when Billy arrives at the house it's suddenly night time.
Continuity mistake: The first night in Billy's room, Gizmo is half a meter away from the Santa Claus hat, but when the angle changes he is just a couple centimeters away.
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: 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: 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 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)
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: A pair of baseballs and several cans appear behind Billy when Stripe attacks him with a chainsaw. (01:32:35)
Continuity mistake: When Mrs. Deagle is killed by the gremlins, throughout the scene she appears to be either bare legged or wearing beige-colored tights. However, when her corpse is on the ground after being launched out of the house, suddenly she's wearing dark blue tights.
Continuity mistake: One of the mutated Gremlins scratches Billy's hand and then grabs an apple. On the desk there is a fake brain. In between shots it goes from being on its side to sitting flat.
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: 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: 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: When Billy is teaching music to Gizmo and the dog is laying on the bed, the wrinkle on the blanket next to the dog disappears between shots.
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.