Click. Click. The two clicks that you hear when pressing the top button on a retractable ballpoint ‘click pen’ are a key to understanding the mechanics happening inside of it: A rotation, extension, and lock of the spring-loaded ink cartridge, pushing the ballpoint tip into place outside of the casing. The two clicks that follow, the sound of pressing the button a second time, rotates and retracts the tip. How exactly does this ubiquitous writing tool work?A Quill from the Museum of Obsolete Objects, The Writer automata by Pierre Jaquet-Droz, The Ingenious Design of the Aluminum Beverage Can, and How is an Etch A Sketch made?