TIL that in South Korea there is a Fan death urban legend.
Fan death is an urban legend prevailing in South Korea in which an electric fan left running overnight in a closed room can cause the death of those inside. Fans sold in Korea are equipped with a timer switch that turns them off after a set number of minutes, which users are frequently urged to set when going to sleep with a fan on.o_O
I love some of the pseudoscientific explanations that exist to try and justify this:
That an electric fan chops up all the oxygen particles in the air leaving none to breathe.
That an electric fan creates a vortex, which sucks the oxygen from the enclosed and sealed room and creates a partial vacuum inside.
edit: it doesn't strictly have to be something you learned today, just something you never knew before and found interesting. It can be something obscure that most people also wouldn't know, or something that everybody knows and yet somehow you didn't.