There are 18 types of windows - what useless facts did you learn from writing your novel?

[Lirina]

As I'm describing Ryvan's parents' mansion, I somehow ended up learning more about windows than I wanted... Here are the window types in case anyone wants to know.

So now I'm wondering what utterly useless facts other people learned when planning or writing their novel

EDIT: Add what you needed to know the fact for

[sorible]

This would probably be useless info to the average human, but if you wanted to kill someone, you can't use a fire knife because it would cauterize the wound and stop bleeding.

[EncryptedWriting]

a french horn unrolled is 13 feet long

[Lirina]

And I didn't even know that fire knives existed...

[Lirina]

What on Earth did you need to know that for?

[EncryptedWriting]

let's say that someone lost something in a french horn and they thought that it would be easier to unwind in order to get a particular item out..

[crowstories]

The phrase "hit the hay" comes from a time when people slept on straw mattresses and would beat them before going to bed to scare the bugs away.

[Audahlys]

Male wolf spiders make a purring noise to attract female wolf spiders. Nebulae (the plural form of nebula) are relatively short lived compared to other phenomenon in the universe as they only last for 10,000 years. There are also different kinds of nebulae like an H II region or dark nebula.

[Lirina]

As someone with an interest in languages, I actually find that useful to know

[Oto_Kouda]

The phrase "the proof is in the pudding" was originally "the proof of the pudding is in the eating," and back when the phrase was created, "pudding" meant...sausage, and not just ANY sausage.

They would like, fill the intestines of an animal with meat, making something that looks similar to the sausage we know now. Therefore, "the proof is in the pudding" really meant "you don't know if [the intestine sausage] is good unless you try it!"

[Lirina]

That's so disgusting

[MasterValkyrie]

A duck's penis can be as long as 16.7 inches.

An adult Dragonfly has a maximum lifespan of 56 days.

[Stargazer31]

The Weddell seal can hold its breath for up to 30 minutes, and dive as deep as 2,000 feet.
The Norse goddess Freya slept with her own brother.
There's a Scottish monster called the Nuckelavee which is like a centaur that has no skin.

[sevenstarsofeightIam]

I did some research for my first novels. I found plenty of data about fairy folklore from around the world. I came away with a long list of 18th century slang. It was all pretty useful.

I did not research my second novel -- I was pretty much making it up off the top of my head.

Same with the third. Since I write on my home computer, when I need a quick answer, I stop and enter a search string.

The Faerie Dusters | Tapas

Star Seeders | Tapas

The Space Bum | Tapas

[Random_Guy]

There are approximately 14,000 known kinds of mushrooms, though this is suspected to be only a fraction of the true number.
These many mushrooms are divided into four categories: Saprotrophic, mycorrhizal, parasitic, and endophytic, based on how they feed themselves

I've also learned the average density of bone, bone marrow, musculature, flesh and other bits and bobs of the human body, as well as the average cubic space of the human body.