In cartoons, you often see mice run into those little arch shaped doorways in the wall. And once inside they usually have a tiny suite of rooms with a little bed, a tiny sofa, etc. I always assumed the second part was pure make-believe, but do these little arch shaped doors really exist? If so, how did they get there?
I can see that if such an opening in the wall really did exist, that a mouse would use it as handy little escape route and furthermore, any mouse living inside the walls might venture out such an opening to find some food…which explains why people are always putting mouse traps outside those little arched doors. But I have never seen one of these in real life and if they do exist, I can’t imagine how they were formed.
On the flip side, if the arched mouse door is pure fabrication, what prompted it?
They are (I think) intended to represent the holes that the mice themselves gnaw in the wainscoting. Real mouse-holes look a little like that. Obviously, nowhere as neat, but, instead, quite ragged. What you’d expect from carpentry done with incisors.
It’s just a cartoon convention, like plunger-style detonators for dynamite, or big bags of money with large dollar signs on the sides, or pies cooling on windowsills (in large pans that say “PIE,”) or the like. Iconography.
I agree with Trinopus that they are meant to represent real mouse holes, which are much more ragged. As for your question of how they are formed, in my (unfortunately rather extensive) experience, they seem to start off as little cracks or gaps that tend to exist in any house - places where trim, doors, or windows don’t fit tightly and places where holes have been cut into the wall for wiring or plumbing are often the culprits. Because of older materials and retrofitting these types of gaps are more common in older homes.
The mice can see/smell what they want (food) through these little gaps, so they set to enlarging them with the only tool at hand - their teeth - until they can squeeze through. This results in the ragged, arch-shaped hole that is represented, in a tidier, cuter way, in cartoons.
That’s my take on it anyways, from personal experience fighting the little buggers. I cannot speak to the veracity of the ‘suite of mouse rooms with tiny couches’ part, I never investigated to that degree!
These things are often rooted in reality (often Victorian reality) though - for example, the plunger-style detonator is the Reliable No. 3 Blasting Detonator. Likewise, mice really did chew holes in skirting boards, and really did raid pre-refrigeration larders for cheese (not their preferred diet, but it’s one of the longest-stored foods and the one that would easily show evidence of being chewed)
Mouse traps baited with cake, chocolate or fruit will be more likely to catch a mouse than those baited with cheese - it really is a just myth that cheese is their food of preference. Of course, they’ll eat it, but not preferentially.
I understand peanut butter is highly effective (I purposely refrained from comparing it against cheese in post #8, because part of the reason it’s effective is mechanical - the mouse has to eat it in situ on the trap, greatly increasing the chance of springing it)
Arches really are a natural shape for a door. Your feet are usually about as wide as your whole body, so you want the widest part of a hole at the bottom, with the width consistent some way up until the body/head narrows. It’s the same basic geometry for arched human doors as it is for chewed mouse doors. Cutting out square corners at the top of a doorway takes extra work that isn’t really needed (especially in the case of mice).
For what it’s worth, I’ve seen mice chew holes through cardboard when I used to raise them. We’d put small boxes (like Kleenex boxes) in the cage. They would either shred a box entirely and carry it off to their nest or they’d start a nest in it. In that case, they would create some holes to make getting in and out easier. These were certainly not cartoon-style arched doorways, but they were rounded holes with flat bottoms.
If you’re going to imagine bedroom furniture in there, the hole is probably the most accurate part of the picture.
Thanks for the replies, guys, and damn is my ignorance fought! I genuinely did not know there was any such thing as a mouse hole. I kinda sorta figured that the little arch doorway was something man-made like the little rectangular holes for power outlets and mice just opportunistically used them to get into the house to find food.
But knowing now that mice do indeed create these little doorways, albeit not as cute and symmetrical as in the cartoons, a few questions: I know that mice can fit thru really tiny holes, so does the mouse just chew a really teeny tiny space that he can squeeze through or does he make something much larger? I seem to remember Jerry (of Tom and Jerry fame) standing upright in his doorway, often wearing a top hat. He also carried enormous wedges of swiss cheese thru these little doorways. I would assume that real life mice just make holes big enough to squeeze through, but given my very limited/nonexistent experience with mice, I could be way off base.
We’re not talking loose-with-the-facts Mutual of Omaha or David Attenborough here, we’re talking the esteemed Friz Freleng. See 
