Midori Carton Opener. This handy retractable carton opener can be used for a wide range of purposes, from opening a package to cutting a single sheet out of a notebook. The cover of the body is retractable hiding a sharp ceramic blade inside and can be opened 180 degrees. Moreover, the ceramic blade can be reversed and used as a sharp new blade if one side gets dull. Plus, it features a built-in magnet on either side of the body so you can attach it to metal furniture or a fridge for smart storage.