Despite the lack of tactile feedback, digital interfaces have a "feel" - and one of trickier elements for this are dropdown submenus. You know them: hovering your mouse over a menu option in a column causes more options to pop out to the right. The trick is that if the submenus pop out too quickly, the interaction is "slippery," and you can too easily slide to an adjacent option and the wrong submenu. So a delay is added, which is effective in preventing these mistakes but makes it feel "sluggish." Well, Ben Kamens has discovered how Amazon's dropdown submenus are lightning-quick and error free: tracking the path of the mouse, rather than its location. He determined that if the mouse moves from a menu option to any location in the colored triangle (shown for illustration here, but not actually visible), the current submenu stays open; if it leaves the triangle, the submenu changes with no delay. So it's not slippery, but it's still quick. It's the GUI equivalent of a tight-cornering nimble sports car - and that's a pretty good feel! Check out his explanation for some good animated examples of dropdown submenus that are slippery, sluggish, and just right.