After thousands of years of human existence, you might think we know all there is to know about the life of girls.
But it turns out we've only just scratched the surface, as Roberto Carlos discovered when he lived with all girls for a week.
Keen to share his knowledge - and not suffer alone - Carlos has taken to Twitter to share his findings with the world.
The thread even had a start time so everyone could prepare for the truths to follow.
Girls can get pretty loud.
They really look after each other. Or at least one of them does.
And they can also be pretty gross... yet organised?
Some pretty weird stuff goes down.
There's no such thing as personal ownership.
Or too much food.
They live life to strict rules.
No boy they text is safe.
Hygiene and time-keeping are taken very seriously.
Being good with eyeliner is a rare gift that should be shared.
Girls have a lot to think about.
Suspicion runs deep.
Hair - and everything to do with it - is an untameable monster.
Sleep is almost as important as food.
Girls have a unique sense of humour.