Fun fact - post something interesting you just learned

One fun fact per post. Keep it interesting.

Any topic works - history, science, space, animals, the human body, food, technology, geography, language, pop culture, whatever. Just has to be something that makes people go "huh, didn't know that."

Short facts are fine. Long explanations are fine too if the topic needs it. Main thing is it should actually be interesting, not just technically true but boring.

Source it if it sounds made up, because some real facts sound absolutely fake. Also fine to post commonly believed "facts" that are actually myths - debunking false information counts as learning something new.

What's a fun fact you learned recently?