Visible crew/equipment: When a gremlin attacks the Mum from a Christmas tree, and the tree falls on top of her, you can clearly see a member of the crew with eyeglasses, wearing a red shirt, standing behind the tree pushing it forward on top of her. (00:54:30)
Revealing mistake: When the professor is trying to find the gremlin, he is in the room with the movie playing. The projector that is playing the movie is actually moving backwards. (00:44:35 - 00:47:35)
Visible crew/equipment: In the scene where the cop car flips over, if you pay attention, you can see the metal plate that's welded under the car that helps it flip over. (01:08:25)
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)
Visible crew/equipment: In the classroom a Gremlin takes an apple, then eats it behind a desk. The Gremlin then throws it from behind the desk. Look closely and you will see the apple is actually thrown by a human hand, not a Gremlin hand. (00:48:00)
Visible crew/equipment: As Mrs. Deagle is walking along the street, carrying the broken snowman head, as she passes one store, clearly reflected, a little ahead of her, is a man carrying the boom mike. (00:10:00)
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)
Revealing mistake: Billy is on the floor about to get attacked by Stripe. You can see the rip in Billy's jumper before Stripe has scratched him. (01:00:30)
Visible crew/equipment: When Stripe is attacking Billy with the chainsaw, when the camera pans to the side right before Stripe attacks you can see a crew member's hand place Stripe over Billy. Also you will notice that there is a piece of plywood attached to Stripe's feet. (01:29:10 - 01:32:55)
Visible crew/equipment: In the bar, as one Gremlin bangs his beer glass on the table, you can see a wire attached to his arm, leading under the bar. (01:10:40)
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)
Revealing mistake: When Mrs. Deagle is visited by Christmas caroling gremlins and one hot wires her chair, as she shoots up the chair, she passes the same pictures on the wall at least four times. (01:09:30)
Deliberate mistake: During the scene with the malfunctioning juice maker, when it goes nuts there is no possible way that all that juice and pulp could have come from just one orange. (00:22:45)
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)
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.