Smallest hole for a mouse experiments

Living in the country, mice are a fact of life. I was curious how small a hole a mouse could get through.

Last year I experimented with a mouse maze, which included a 19 mm hole that the mouse had no problem getting through. So the question was, how much smaller a hole could a mouse get through?

So I built this device, which has three cubbies where I can put food, and a board in front with different sized holes. I can move the board to adjust which sizes the mouse can try to get through to get at some peanut butter in the cubbies.

I set this up in a shed where I don't mind mice as much as in the house or in the workshop. The set-up was illuminated continuously by some LED strips. A Raspbery Pi computer with camera module was constantly watching, saving the images if there were any changes.

And soon a mouse came. It was able to get through the largest hole (19 mm), and the next smaller hole (17.5 mm). But not the smallest hole (16 mm).

I wanted to see if the mouse could get through holes of intermediate sizes, so I made a 17 mm hole and a 16.5 mm hole. I don't have drills of those sizes, so I used my pantorouter with a circular template to route out these holes.

But it seems the mouse was not willing to play this game. It went in the 17.5 mm hole (which it had gone in earlier) but didn't really try the 17 mm and 16.5 mm holes. It only ate the easily accessible peanut butter that I kept adding to tempt the mouse. Eventually I stopped adding peanut butter, and then, for about two weeks, the mouse went away entirely, so when it came back, I made sure to keep adding peanut butter to my contraption to keep it trying. But it seems the mouse figured out that it could get peanut butter without actually trying to go through the smaller holes.

But then I had another creature show up. First I thought it was a mole, but it's actually a shrew. Shrews look similar, but don't have the large front paws.

The shrew tried getting through the holes with much more enthusiasm than the mouse, but its larger size was a problem.

But with a lot of persistence, and a lot of wriggling and squirming in the holes it was able to get through the 17.5 mm hole, and then even the 17 mm hole! That's a smaller hole than the mouse tried to go through!

In the meantime, the mouse kept making an occasional appearance, but the shrew kept eating any easily accessible peanut butter. With the mouse too lazy to try the holes anymore, it didn't get much.

I'm pretty sure mice can get through smaller holes than 17 mm, but the smallest hole for a mouse is probably not as small as I thought. 13 mm, or 1/2" is probably too small for an adult mouse.

Making the video

Though the video is only a few minutes long, it actually took over 1000 hours of filming to get the shots that I used. Sometimes days went by without the mouse making an appearance, and it only showed up briefly every day. I used my imgcomp program to detect motion and save the appropriate images.

My camera set-up didn't record sound. But as a silent film, it wasn't that interesting. I searched the Internet for some sound effects to add but couldn't find what I was looking for. So the sound effects (but not the music) were all made by me. Most I made with my mouth or by scratching or tapping my fingers on my desk. The squeezing through the hole sounds took the longest to figure out, but rubbing my fingers on a balloon made a very satisfying "squeezing through" sound effect. Once the mouse made it through a hole, I wanted a popping sound like a champagne bottle, but less sharp. Slamming my palm against the opening of a small glass jar made just the right sound.

With so many clips, and all the sounds to add, it took several days of editing to put this together. But every time I watched some of the clips, I couldn't stop laughing. So I'm hoping this video will have a similar effect on viewers and that the extra effort becomes justified. My previous mouse experiments have been very popular, and so far, YouTube has not demonetized them even though they tend to crack down on stuff that anyone might find remotely offensive.

Mouse update: Two days later, the shrew managed to squeeze itself through thesmallest hole!

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