The new MacBook and MacBook Pro don't just want to impress you with their fancy new fabrication techniques, unibody designs and bolstered performance: they want to make you more honest, at least when it comes to reporting water damage. According to the service manuals, the new line of MacBooks include submersion sensors, designed to indicate if the laptops have been exposed to excessive levels of moisture and/or dropped in your toilet.
Phones, including Apple's own, have been fitted with these little stickers for years, but they're a rarity in laptops. You might want to think twice before you forget to mention the "used as a prop in an elaborate college drinking game" part on your next Applecare claim. Thanks, Justin!