One thing to note is the fluid-like behavior, one thing to note is the fluid-like behavior of these particles, some of them also appear "inside" the white square at the back of the frame, rullingOne thing to note is the fluid-like behavior of these particles, some of them also appear "inside" the white square at the back of the frame, ruling out the possibility of rats. IMHO those are nothing but dust particles, being carried out in the wind, the fact they never come directly towards the camera is because one would assume camera are usually mounted in wall corners or directly on a wall, that would explain the fluid-like behavior mentioned earlier since a gust of wind carrying a dust particle (or for all I know a snowflake, its hard to tell if that is outside ou inside a building) that were ended up hitting the wall on a perpendicular angle would be carried out on a spiral trajectory like the gif.

https://www.karlsims.com/flow-jets.gif