How do you explain to students how membranes work? Well, you can draw pictures or use computer animations like the ones below. You could also do what Mr. Keller did today and run into a wall, literally. His point: some objects can permeate some membranes, if they are small enough. While he was small enough to walk through a doorframe, he was not small enough to permeate the wall. Good teaching sometimes means using unique analogies to help students find truths. Thanks for being a good teacher Mr. Keller!