There is an episode of The Dollup podcast about ninjas in 1800s (I think) Japan and in one part they talk about how the ninja would often have to wait around all day or more hiding to assassinate someone. They way they could tell how long they’d been waiting was by the change of the “dominant” nostril.
Apparently even when not stuffed up the air passes thru one nostril more easy than the other when you breathe. It switches about every 40 minutes.
I did not know that. Very cool piece of info to learn. Thanks!