I sometimes feel guilty when letting my fingers do the walking in reporting these days, but if you try sometimes you can get what you need online and in books. Take my take on the Oreos centennial — judging by James Trager’s “Food Chronology,” those iconic black-on-shortening wonders originated as a knockoff of the now-long-gone Hydrox cookie. That was the “biscuit bonbon” that came into stores first. And it’s the dark secret you won’t find anywhere in the expanded press releases and blog blowouts everywhere on the anniversary. Instead, look, over there! It’s a factory tour.