Visible crew/equipment: In the scene where Lars is in the string factory alone and the machinery pulls on loose threads on his clothing, there is a shot where a crewman's arm can be seen through some mesh holding the thread.
Continuity mistake: When Ernie picks up the cereal pack and walks to the table, the mouse has chewed a hole in the pack, and cereals drops on the floor (the whole pack of cereals). And later in a shot from a different angle, the cereal is gone.
Audio problem: When Catzilla is chasing the mouse and gets stuck in the mousetraps and starts meowing, if you look closely at the mouth, the cat isn't really meowing at all.
Plot hole: It takes less than 3 minutes to fill the house with water using a mere garden hose? I mean come on...
Continuity mistake: When the brothers go into the attic, there is a large portrait facing away from the walls that it is propped against. They open a box and moths are released. The fat one gets hit by a pole, and wanders across the room. He then appears with his head through the painting. His head would have gone through the painting the other way, as it was facing us, not the wall.
Continuity mistake: When Ernie is auctioning away the house, he has two papers on the table, but when he falls three papers fly in the air.
Other mistake: When the rat catcher is dragged through the house by his safety harness, he starts off being dragged face upwards, but a couple of seconds later his position has changed, he is now face downwards and at the end of this he is face upwards again.
Continuity mistake: In the scene where the mouse is trapped behind the skirting board by the nails fired by the nail gun, we see at least 5 nails, yet on the exterior shot of the same skirting board, where Lee Evans is about to hammer in a protruding nail, we only see 2 nails in the board.
Revealing mistake: When Ernest is climbing up the chimney to get the mouse, the chimney shakes/wobbles slightly, showing us that it's made of rubber.
Revealing mistake: When the mouse chews the rope to make the little elevator fall with Catzilla in it, in the shot where the elevator is going to fall you can see that the cat has been replaced by a fake cat, before the elevator drops.
Plot hole: Before giving his father's piece of string to his brother, Lars kept it in his suit's pocket, however in a scene in the factory, we see that Lars' suit gets entirely destroyed and yet later on in the film, he somehow has the string.
Answer: There's not really an answer, because the film has sort-of a nebulous timeframe given its cartoon-like atmosphere. Ex. Everything is old fashioned in design, including architecture and clothing, but current technology is also present. It's not really meant to take place in the "real world" or a specific timeframe, so much as be a silly throwback to old comedies and especially old Laurel and Hardy films. So, the best answer to your question would be that it just sort of exists in its "own" time, so to speak - an amalgam of different time periods all put together for maximum comedy impact.
TedStixon
Adding to this, the Wikipedia page on this movie states that... "The film is set in a humorously indeterminate 20th-century time period, with styles ranging from the 1940s to the 1990s."
Quantom X ★
"Mouse Hunt" was not modeled on 1930s Laurel and Hardy films so much as it was a direct retread of 1940s "Herman and Catnip" and "Tom and Jerry" cartoons, which spawned many knock-offs over the decades, from "Coyote and Roadrunner" cartoons to live-action comedies such as "Home Alone" and others.
Charles Austin Miller