Face masks are an important tool for curtailing disease transmission, and this video explains how even imperfect masks do a much better job of protecting people than you may think. Strictly speaking, this video is not fluid dynamical — fluid dynamics plays more of a role in the details of what makes a mask effective — but the video is so good and so timely that I just have to share it. Given it a watch and then go explore the interactive essay to get an even better handle on mask mathematics. (Image and video credit: Minute Physics; see also The Multiplicative Power of Masks)