-40 is the same in C and F... I know this because I grew up in Wyoming. I've seen -40.
At that temp, you can do this neat little trick where you take a pot of steaming water (not boiling, that's a safety issue) and throw it into the air.
It will be snow before it hits the ground.
Again, don't use boiling water, and don't even try it if the temps are above -10 F. Don't throw the water into the wind, that will just splash it back onto you, and if you ignored the "don't boil" instruction, you'll be splattered with boiling water.
-30 is pretty normal in Alberta through the winter. It’ll even drop to -40 for a week or two a year. People mostly stay inside, and they plug in their cars so their engine blocks don’t freeze. Cities usually invest heavily in snow plows since they use them so much each year, and everyone has snow tires. There are lots of indoor places to walk around, and downtown Calgary even has a series of “Plus 15s” which are tunnels from one building to the next, about 15 feet off the ground.
And they complain that the west coast is too rainy to leave.
When it's like -50c with the windchill, social things are pretty shutdown, but businesses don't close. School buses don't run, because they don't want to be held liable for kids freezing to death.
When you are risking death by going for a walk, you don't go out unless you need to.
Happened in Chicago a few years ago. It sucked a lot and all the efforts couldn't keep our shitty apartment pipes from freezing. But at least I have a very cute photo of my dog bundled up and ready to go out. So there's that...
Double digit negatives is where you start to realize that nature can kill you with complete apathy. Just breathing hurts. You must cover your face or risk frostbite in a surprisingly short time frame. The scarf or mask you have wrapped around your head to keep your ears from freezing off directs your breath past your eyes. The moisture in your breath then freezes on your eyelashes and eyebrows. I have had to blindly pull my gloves off to free my eyelashes from the frost that has frozen my eyelids shut.
I once spilled a bucket of water on my leg in double digit negatives. (Hoses are not an option in such weather and animals still need to drink. ) The water froze my pant leg solid within a minute. It was a very uncomfortable waddle back up to the house.
That sounds absolutely miserable. I know someone who used to live in Alaska and they said you could throw a hot cup of coffee into the air and the liquid would freeze before it even hit the ground. That sounds ridiculous to me, but after reading your comment, I'm starting to believe.
In my area, the coldest I've experienced is ~5F (-15C) and it's usually above freezing, so I'm used to running outside to grab the mail or whatever in shorts. Then I went to my sister's house and it was -13F (-25C) and tried doing the same. So much regret.