When Apple unveiled its 2015 MacBook, reviewers quickly discovered its keys were flatter than ever, with single-digit millimeters of travel between their pressed and unpressed states. At first, we heralded this as a miraculous accomplishment in ever-thinner laptop computing, which carried over virtually unchanged into the next years' models. But all was not well. The complex 'butterfly' switches that enabled the incredibly-slight travel distance had kept dirt out -- until it got in and had nowhere to go, mucking up keys and effectively disabling keyboards, according to some reports. It seems Apple filed a patent for a contaminant-proof keyboard back in 2016 to solve the issue.