Way back in iOS 3, Apple implemented the “shake to undo” feature. This means if you’re typing, say, a text message, and you want to “undo” your text, just shake your iPhone, iPad, or iPod Touch. While it’s a cool trick, this isn’t the most usable feature that Apple has ever implemented. It’s both hidden and unintuitive. And I’ve definitely triggered it more accidentally than I have on purpose.
Quento (iTunes link) is a stylish puzzler for iOS (and Android, and Windows 8, and Chrome) that looks a lot like Letterpress except it substitutes simple math problems for word problems. It’s a good distraction for your brain, but unfortunately it’s also a good example of how not to implement a shake feature in your game. Shaking your phone resets the board, causing you to lose all your progress for that level – without any warning.