Most interactions have an underlying rhythm. For example, an application may ask you to scan a list of items, then click one, leading to another list to scan and click. Scan, click, scan, click. You can get into a groove. Systems increasingly have rhythm too: animated transitions, hover responses, and digital physics. Static is so last year. But sometimes it's wise to break rhythm. And besides, rhythm alone isn't enough. The best experiences induce a state of "flow," during which users get into such a groove that mechanics disappear, time falls away, and the experience itself becomes intrinsically rewarding. (Wouldn't that be awesome?) Designers own rhythm. Yet our work practice lacks appropriate tools and vocabulary. How do you portray a groove in a wireframe or PowerPoint deck? Examples from other fields can help. We'll see how it's done in animation and movies, game systems, music and choreography.