TIL about a thing called laminar flow. It happens when fluid flows in infinitesimal parallel layers with no disturbance between them, giving the impression that it is not flowing.

https://en.wikipedia.org/wiki/Laminar_flow

https://www.reddit.com/r/todayilearned/comments/156lpe3/til_about_a_thing_called_laminar_flow_it_happens/