Visible crew/equipment: When Billy's mom takes the picture of Gizmo at the beginning, Gizmo becomes frightened and runs over to Mr. Peltzer. When the scene is slowed, you can see the puppeteer's hand underneath while operating the Gizmo doll. (According to MM's rules, the use of slow motion is permitted when the mistake is something significant.)
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.
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 continuely change shape and size. And if Stripes claws were sharp enough to cut him that bad then how come it didn't cut through his white t-shirt under his sweater. Because Billy showed alot of pain when he was clawed.
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.
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.
Plot hole: When Billy is talking to the Sheriff and his Deputy, he explains what the creatures are, and shows them Gizmo. The cops don't take Billy's story seriously and even mock him, even after the phone call about the Futterman's Snowplough "accident." Why didn't Billy simply tell the Sheriff about the dead Teacher or get them to call the Dr where Billy left his injured mother? The mere mention of a dead body should have to be investigated by the police, and the word of a local respected Dr should also be enough to back up Billy's story and give him the help he's need to stop the Gremlins.
Add timeThe Rodent
Revealing mistake: In the scene with the malfunctioning juicer, you can see the actor who plays Billy is about to laugh right before all the juice explodes out of the machine. As that is happening, you can see he has broken out into a full laugh. True, he might be showing some mirth over another one of his father's malfunctioning inventions, but he was about to break out into laughter before anything happens, and his laughter is inconsistent with his frustrated demeanor when Pete walks into the kitchen.
Revealing mistake: Just after the mum liquidises a Gremlin, she then has to deal with one throwing plates. If you look carefully, whenever the plates are thrown from the Gremlins perspective, whenever its left arm comes into shot, you can see the puppeteer's rod used to move it.