Why is it in Hollywood movies every time there is a vent or AC unit someone has fixed little ribbons on it? Is that a thing americans do? Why? The vent in this movie is close to the floor in the toilets of a train. This implies someone got on all fours ON THE FLOOR OF A TRAIN’S BATHROOM to stick those ribbons there for a reason i can’t even begin to comprehend.
I often see them in offices. People who working 8 hours in an environment where that don’t control the AC will often want proof that it is or is not working effectively. As there are potentially multiple vents along a duct these ribbons are a handy way to see how much the duct pressure varies across the room.